Street Fighter X Tekken leaked because of DLCBy
After the whole ordeal with the DLC for Street Fighter X Tekken, including on-disc DLC and removal of videos with DLC characters, it seems like some of the fans have had enough. Full leaks of Street Fighter X Tekken for the XBOX 360 have sprung up on several torrent and file sharing sites. The PS3 version is unaffected because BluRay makes it much harder to pirate games, including Street Fighter X Tekken.
Of course, it would have been a matter of time until the game was leaked anyway, but pre-release and even first day leaks are not very common.