IE's problem is probably because many large companies have standardized on IE and to be 100% compliant could create backwards compatibility issues with sites built to work with the non compliant issues.
Not true... that's why you then have two rendering engines: quirks mode and regular. Sites that are not validated (which takes all of 10 seconds to check) would render in the new IE "Quirks" mode which would be the old engine. If it validates, then it uses the new standard engine.
Or, the old pages just need to add a comment that IE looks for. Something like:
<!-- if[IE7] Quirks -->
I love the tag-line they're using:
We heard you...
you wanted it easier and more secure
The same could be said about many of its products 😉
But I still see no reason to switch from Firefox/Opera 🙂