What’s broken when a server requires the www before the domain name.
Example:
pinballmachine.com does not work
www.pinballmachine.com works
(I think I fixed one by complaining.
newark.com now works)
Nothing is broken. It just means that it isn’t configured how you want.
Either the IPs for www.domain.com and domain.com are set to different values, or the web server is not configured to serve the same content for both domains.
You can check the former by doing an nslookup or ping of the domains and seeing what IPs they resolve to. If they’re the same, then the latter is probably the cause.
The www. prefix indicating a web server (as opposed to an ftp server, for example) is just a convention. Traces from before the convention was established do exist: web.mit.edu still functions, mirroring www.mit.edu
The Internet is used for many different things, and the Web was not always the biggest (or even one of them at all). So MIT would have, for instance, a server for FTP, and a server for Gopher, and a server for SMTP e-mail, and so on. These were probably called something like ftp.mit.edu, gopher.mit.edu, smtp.mit.edu, and so on. When the Web came on the scene, they added a new server for that, too, and called it web.mit.edu (MIT was, of course, an early adopter, and at the time they set that server up, “www” wasn’t yet standard). If you just tried to access mit.edu , it wouldn’t know which of those servers you wanted. Nowadays, the Web is the most common use for the Internet, so most sites are configured to assume that you want the webserver, and site.com will take you to the same place as www.site.com . But depending on the site, it might not be wrong to assume the FTP server as the default, or something else, or nothing at all. In that case, going to site.com without the www would give you an error message.
Sadly, many sites where it would be perfectly logical to forward the request to the www. site do not do so. One I’ve encountered recently - dfes.gov.uk fails to connect to www.dfes.gov.uk, and the added problem here is that the suffix has to be typed manually, rather than relying on Firefox to add the ‘www.’ and ‘.com’ to something typed into the address field.
Here’s another relevant example. www.straightdope.com goes one place, while boards.straightdope.com goes another. For all I know, there’s a mail.straightdope.com out there as well. straightdope.com goes to the same place as www.straightdope.com, but only because somebody took the care to define it that way.