Christian Svensson gave a few more details on why cross platform play won't be a reality for Street Fighter 4. Here are his comments, along with a few other subjects from the Unity Boards.
Why won't there be cross play between XBox 360 and PC Street Fighter IV players?
Sven: Supporting crossplay in any game is not trivial by any stretch.
It also means a commitment to version locking where if you update one platform, you have to update the other too. And costs of doing so are also not trivial.
Additionally, schedule is a factor. If we wanted to go that route, it would have meant an even greater delay in the product arrival.
Will the PC SF4 game have improved net code?
Sven: To the best of my knowledge, it's identical net code.
Is there any chance of Capcom re-releasing Rival Schools?
Seth: Re-releases are not always as cinchy as they sound, but I do agree [Rival Schools] has some fun potential to reach an audience. The downside is that time has not been as kind to its 3D graphics, and while sprite-based work can still seem interesting and even nostalgic, some of the Rival Schools models just look a little rough.
We've also got a LOT of fighting options available right now, so we want to be able to focus on each of them without just flooding the market with our entire back catalog. [...]