We know the reason. Well, more or less. Its not HTML5. Its not Apple vs Adobe. Its AT&T.

“What’s also big is the exclusion of Flash. The reason is obvious. No flash, far less streaming over 3G. Less streaming over 3G means less bandwidth consumed. Less bandwidth consumed means AT&T can offer a great price on the 3G data service. I personally have never had problems with the AT&T network. The limits on 3G streaming probably mean I won’t going forward either. That’s a good thing.”

Source: Marc Cuban, of course.