No it is not.. go ahead and try to validate google.com Hmm . 46 Errors, 3 warning(s) Google does not even validate and comes up with a bunch of errors. Guess that if Google does not validate then they can't ask our sites to validate... See for yourself http://validator.w3.org/check?uri=w...(detect+automatically)&doctype=Inline&group=0
It's not .. But if you can do it, why not? anyway, you get a buch of errors especially when you use JS ..
W3C validation is all about using good principles and making sure your pages work now and in the future as you had intended. I always try to validate my pages in the same way that I try to ensure that I use correct spelling and grammar. It's also useful as a debugging tool too.
Google does not say "wow, it validates so give him a boost", but what good is the traffic if the page is broken?