It’s aesthetics and tradition. Read: inertia. Ditto, British taps.
It’s Darwinian principles at work: they’re that way because they’ve always *been *that way, and there’s never been a compelling reason to change them.
When we have this discussion about natural selection–“Why aren’t rabbits green?”–the answer is the same: because brown works.
Next question.
There’s one other problem with door knobs I’m surprised nobody’s mentioned ('less I missed it): the greasy hand trap. I don’t know how many times I’ve been imprisoned in my bathroom until I could rub the moisterizer thoroughly in. Maybe my doorknob is too tight, but I’m pretty sure that this would never happen with a handle.
As for the mass production theory? Bah. You have to show me how mass production impedes innovation. Generally it works the other way (everything’s cheaper to create - including alternate varieties and styles. This is why there’s 300 varieties of cereal in the grocery store).
I think you will find this post violates every basic principle of the economics of manufacture and market. Well, OK, maybe just a few of them.
The larger the market, the easier it is to manufacture something that appeals to only a segment of the market and still make a profit.
Or why British books have the titles printed the other way on the spine.
No, it’s every. You were right the first time.
I wasn’t aware that there was a different international standard for either of these things. On British books, if the title/author is printed vertically on the spine (e.g., you have to tilt your head to read it), the bottom of the lettering would be pointing towards the front cover?
And what other way would a lightswitch work? Up means on, doesn’t it? This is upsetting my entire perception of the world…
No, down means on!! Yes it does! We’re right, you’re wrong, nurr nurrr I’m not listening… 
Doorknobs are a lot more attractive, and yes people will go for looks over function (think of a lot of those designer clothes). As has been said, all public buildings have handles. Our office actually has bars running the width of the door you push to open it, which is due to the doors being made for easy access to the office if there’s a fire (they’re always unlocked as well).
Another option are the thumb latch handles, which you depress the mechanism with your thumb:
http://www.blksmth.com/Cdoor_pulls_&_latches_1.htm
The one’s I’ve seen on modern doors are more on interior doors than outside.
Good answers everyone.
I doubt it is a production scale issue or shelf space in stores. Going into a just about any hardware store or looking in a catalogue shows that there are thousands of different handles (or knobs). Ok maybe there aren’t a thousand different handles/knobs in one store, but you know what I mean, right?
I’ve never seen things getting caught on the handle as being a major problem (not even a minor one). But hey maybe it is in the US.
Admittedly it has been been a while since I last visited the US (in 1998 I think), but door knobs were present in the hotels I stayed in then. Maybe they weren’t compliant or they didn’t care.
I guess Lissener is right. Inertia, tradition, different tastes.
It’s still a bit puzzling though. 
Okay, in an effort to get a handle on this question (sorry!) I have been googling around for any information I could find about doorknobs. Although “history of doorknobs” is frequently used as a joke in bios, I did find antique doorknob collectors such as The Antique Doorknob Collectors of America, whose website has pictures of antique knobs, stories about other people’s knobs, and tips on cleaning your own. Don’t laugh.
The best information I could turn up was that doorknobs were not originally mass-produced, of course. During the late 19th - early 20th century knobs were specially designed and sculpted to the architect’s specifications for many public buildings. Examples given were the Missouri Pacific building and the St. Nicholas hotel, both in St. Louis. Each building had custom-built doorknobs featuring a monogram or seal unique to itself.
Many of the ADCA photos are of round knobs with elaborate designs, some made evidently out of glass, ceramic, or clear resin; I imagine roundness was preferred here as it was a stronger shape. Others look like old brass, possibly. Some are oval.
What does all that mean? I dunno. I tried to gather a bunch of information on it in the hopes that something would stick. There might be some evidence that what the architects and sculptors did in that time period has had a long-lasting impression on what the market wants. I haven’t found what kind of doorknobs were around before then, though. Somebody can take it from here.
Oops, sorry for the double-post. Forgot to mention something.
Wikipedia’s article on doorknobs points out that door levers are much more useful than knobs when the center mechanism is situated close to the door jamb. That is, a doorknob in the same position would cause the user to bark his knuckles on the frame.
If the doors in Europe are designed this way (both new and those already installed), with the handle slightly closer to the edge, then a doorknob couldn’t replace a door handle and it’d be nothing to do with style or fashion. You’d have to replace the entire door to convert from lever to knob. If true, it might at least explain why Europe only seems to have levers.
Or with your, you know, elbows. Or forearms. Or pinkies. Or the small of your back.
I hate doorknobs.
Listen, limey, we invented the lightbulb, I think we know how switches are supposed to go. Your whole country is on crack.
Well, assuming you’re talking about Washington (the state in your location)…nope. The UK is about the size of Oregon, which is bigger than your whole state.
Being a good Freudian - I’m sure the whole thing has something to do with repressed sexuality.
Think about it the doorknob looks like the end of a…but then again, the door handle itself looks like a…
Never mind - Now I am not only repressed sexually but totally confused regarding my repressed sexuality and its orientation regarding door opening devices.
I’ve decided to remain inside my house until I can get one of those automatic doors one finds in grocery stores and old Star Trek episodes.
1.) I’ve never had a problem with round doorknobs, unless they’re broken.
2.) Our house is over 40 years old, and a lot of doorknobs have been breaking lately.
3.) When our bedroom doorknob broke recently, Pepper Mill asked me to replace it with a door handle, which she thought more practical.
4.) I did. The door handle kit is made so that you can make the handle face either way, so this comment:
doesn’t really apply.
Er, perhaps not. Ever heard of a geezer called Sir Joseph William Swan? His patent for a light bulb was filed about a year before Edison’s which nicked his ideas, as determined by a British court when Swan sued Edison for infringement. Details here. As a result, Edison was forced to take on Swan as a partner in what became the Edison and Swan United Electric Company.
Up is definitely OFF.
Anyway, I only popped into this thread to remember being very embarrassed as a youth only in the 1970s seeing advertisements for a shop called “Knobs and Knockers” in the King’s Road (and there’s also one in Dublin). Imagine my disappointment when I discovered they sold door fittings.
I wonder if the people who make [urrl=http://www.cafepress.com/alllies.32238547]this product know that they need to make a different version for right-pondians.
Arrrrgh!
I guess this is very “butter battle” but you are wrong.
How do you not *feel *the wrongness of up is off?
It’s like picking up a package, when you pick it up you are active with it and when you set it down you are done with it and can walk away. Up = active on, Down =done=off.
The boys in the back room can go round and round but I assure you up is on and down is off. 
Oooooh…a British court, you say? I call shenanigans!