IIRC, most American commercial breweries and even larger microbreweries pasteurize at least their bottled stock to make it more commerically available - stores and bars can stock it unrefrigerated, etc. (Sprecher in Milwaukee, Wisconsin is one exception I can think of off the top of my head.) I have no idea if they pasteurize the kegged stuff.
Originally, this was to help them with distribution as keeping the beer cold during transport was prohibitively expensive and/or too difficult - remember that many of these breweries had nationwide selling in mind as they expanded, but the sheer size of most US states much less the whole country made that difficult to do.
I haven’t any idea what you’re asking here. Do you mean, do the bars have more on tap than lager, or do they have more than one kind of lager on tap, or what? I’d say the answer would be “usually” and “yes” respectively.
Most bars I’ve been in offer draft beer in pint glasses as well as a smaller glass. If you mean bottles, most all American beers are bottled in 12-oz bottles. (As a homebrewer, I buy Grolsch swing-top pints by the case and use those for my brewing.) I assume that’s because the standardization of that size just makes it easier for them to produce, distribute, and sell their product - it’ll fit in the same shelf space as any other beer, and so forth.
The problem is, the beers that are commonly known as “American beers” are those made by companies which can afford to distribute worldwide; these are the big commercial breweries that produce the watered-down stuff that’s cheap to buy, somewhat lower in alcohol content, and of a certain plain flavor that’s not terribly interesting. Plus I understand that one apparent problem with transport is usually this is beer that doesn’t respond well to aging, and it’s being shipped (literally) which means it’s not going to be all that fresh when it arrives.
Meanwhile Americans hear a lot of “European/British/German/etc beers are so much better than yours” and of course we’re apparently getting the equivalent of what we export getting sent back to us, for the most part. I’ve even heard stuff from friends like how the version in the “home” country is a lot better than the version we get - not sure if that’s due to aging or what. Perhaps the joke I heard is true: “The Guinness brewery has three expert tasters that sample each batch. If the first taster rejects a batch, he has another taster try it, and if he rejects it, he sends it to the final taster. If he rejects it, it gets shipped to the US.” 