There is a reason that the idea that a browser is not considered "real" by some unless it is fully W3C comply. If a browser complies with the standard, a web-developer/designer can write pages that also conform to this standard. In so doing, this developer/designer is assured that their client's websites will be displayed exactly as intended. Granted, most browsers are more or less the same, there are differences. Netscape uses <frame frameborder=yes/no> whereas IE/W3C standards (currently) use <frame frameborder=1/0>. For a web developer to get their site to look how they want it (which can be integral to the viewer seeing anything on the site at all), they have to include twice the tags for certain things, and have to review and test the changes in several browsers. If IE, Netscape, Opera, Konqueror and every other browser at least conformed to the basic W3C standards, there would (ideally) be no need to debug with other systems.

This is also more important as WAP-enabled devices begin to proliferate throughout the populous. So that standard is important if WAP is to go anywhere, because otherwise no one will write for it, thus there is nothing to use on it, and no reason to buy WAP-enabled devices.

HTML is of course a different story, but the reasoning is the same. Of course, getting a site fully W3C-compliant in HTML, CSS (and anything else, I would assume) can be a pain the ass.