What you heard is called a rumour. Tekken 6 may well end up on 360. As of now we don't know.
I'd say 360 fans are deprived of top-tier fighters having only Dead or Alive but they just got Virtua Fighter 5 for the PS3 so they have one top fighter now at least.
DoA4 has a lot of depth.
Not VF depth, but it's not the button masher that people who haven't played it properly call it.