We know SFII HD was causing problems for the development team at Capcom. They've got all these lovely HD textures and sprites they want to use, you see, but Xbox Live Arcade's file-size limit means squeezing these into the 360 version has been a big hurdle to clear. Note I say big. Not insurmountable. Capcom's Seth Killian:
I can officially say that the filesize will not be an issue. With great help from the guys at Microsoft, we will be able to offer the same features on both platforms to the same quality as each other. To use the term I've been reading on the forums, neither console version will be "gimped" due to any kind of limitation.
Breathe easy, 360 owners. Unless you've still got concerns over the 360 controller's suitability for this game, that is. In which case, continue breathing frantically.
Super Street Fighter II Turbo HD Remix: State of the Union [Capcom]