I think Nintendo's showing at this year's E3 showed that they know what they need to do for the next generation. I believe Nintendo is smart enough to know that when you've got the least amount of 3rd party support, you can't release a radically different system that would essential make ports impossible. Especially when the specs between your system and the competion's is (allegedly) virtually identical.
In other words, Nintendo probably isn't going to make it so that the Revolution's controller hooks up to your nostrils, and gameplay is controlled by sneezing.
Besides, didn't Rick Powers hint at the Revolution being backwards compatible?
Rick Powers = Infallible