in reply to (OT) Internet. Who should conform to who?
the only real good answer to this is to look at the stats for your particular site. if 60% of your audience is browsing with Mosaic 1.0 on VMS, you should probably code your stuff to work with that browser (ie, no css or http 1.1).
ignore the stats people toss around about IE being used by such a huge percentage of the population that you can safely ignore other browsers. most likely those stats were collected by other sites. read your own logs and ignore everyone else. eg, on my site, a good 30% or so of the visitors are using mozilla, way higher than what most other people report seeing.
either way, there's almost no reason not to code to standards. if you keep your markup as logical as possible, keeping all the styling in the stylesheet, and use the @import trick, you can make html+css degrade gracefully in almost every browser. IE5+, mozilla, opera, and any future standards compliant browser can get a nice looking site. NN4 can get a default stylesheet with maybe some very basic color and text styling but no positioning. browsers that don't support CSS get nice lynx-like layouts.
complex table-hacked layouts are the first ones to break anytime a new browser or browser version comes out.
so in general, to bring this back away from webdesign and more on topic, you should code to the standards as much as possible but don't ignore what your users are actually using. if you write code that won't work on the target system, even if it's really the target system's fault for not being compliant with some standard, you're going to get burned. and ignore all statistics that aren't directly gathered from your own userbase.