you assume that most websites care about standards. They don't.[1] Writing truly standards compliant html is too much hassle for most people out there, and brings next to nothing in value. What they do is test it against the important implementations: On the desktop IE 7+, Firefox 3+, Chrome. For mobile sites they test for both webkit flavors, and that's it.
Again, IE mobile is facing the same problems as Opara: Both are very decent browsers, but they have different ways of handling the strange corner cases in the tag soup out there than the market leaders.
errata: The web has become a lot better w/r to standards in the last couple of years. Like I said before, I've encountered very few glitches with IE7, and none so far with IE9.
> Writing truly standards compliant html is too much hassle
> for most people out there
This may be true (the "too much hassle" part), but writing standards compliant html is very easy. Or just easy, depending how semantically clean you want it to be.
> and brings next to nothing in value.
This is wrong. Unless savings on network traffic, time spent on maintenance and page load times are of now value to developer.
