This is an unexpected treat: Windows Phone 7's SDK came out today, and apparently it includes DivX support up through DivX6. That means no DivX7, but it's still a lot more than you can find on the iPhone.
While the move decidedly puts Windows Phone 7 way ahead of the iPhone in terms of natively supported media codecs, it's still unclear what the allowed maximum resolution will be. But so far, add it to the list of things that we've found out today about Windows Phone 7 that have exceeded expectations. [Microsoft Visual Studio Developer Center, thanks Daniel!]