Let me make a few random assertions:
(a) A document should *not* be considered validated merely because a
browser (any browser) can handle it well.
(b) All World Wide Web browsers should properly handle all documents
that have been properly, legitimately validated.
(c) If an information provider is serving documents that have been
validated, he/she can be assured that all World Wide Web browsers
handle them correctly.
(d) If a certain browser supports certain formatting features, quirks,
options, or black magic above and beyond the specified formatting
language, the information provider who is serving validated
documents should not care at all, as it does not affect the
information consumer's view of his/her documents regardless of the
browser the information consumer is using.
(e) If a certain browser supports certain formatting features, quirks,
options, or black magic above and beyond the specified formatting
language and it turns out that many information providers *choose*
to take advantage of those features even at the expense of making
it difficult or impossible for other browsers to properly handle
their documents, then this is proof that such a feature deserves
very close inspection as something that should be a standard
supported feature across all browsers: "the market has chosen".
(Now donning my fire-proof bodysuit... :-)
Cheers,
Marc