PC fight fans have been holding out hope for months now Super Street Fighter IV would make its way to the platform, but sadly we have to let you down. Series producer Yoshinori Ono has stated in an interview while sales of the original game were strong, it was also a "number one in piracy" (and this is despite a standalone benchmark release, so that rules out the demo argument), and therefore a PC release is very unlikely.
Ono was sensible about the issue, though, saying he knows because of the widespread piracy, the game received more attention. Nevertheless, Capcom is protective of its properties, and doesn't want the game being "free" in certain regions where piracy rates are high.
He did state if they found a powerful copy protection solution, they would consider it. Steamworks is generally seen as a safe bet by publishers, but Ono would rather not release it at all than as a Steam exclusive for those that couldn't purchase from the service (region restrictions, no credit card and/or PayPal account for the young ones, etc).
As with its predecessor, Super is already running on a Taito DirectX-based Type X2 arcade board, meaning the PC version is already 99% ready. This does make it puzzling they haven't decided to release yet, even with high piracy rates. One possible solution we'd suggest is releasing it digitally only across multiple services to save on costs -- the NPD Group revealed yesterday PC digital sales have surpassed retail, after all.