If you read about the PS4 witch will not be called the PS4. More on the lines of PS "life". It is a PC. It will use AMD type scorce code for its graphics. So if you can make a game for the PC, you can make a game for the next gen PS. It is the 720 that is the odd man out. It has its own type of code so useing it and coding for it will be new and finding the bugs and what not will be harder.

It will work on the PS3 the same way it will work on the next gen PS, it will just need a patch for new graphics and input. It would be just like if you got a new PC, and need to update all the drivers. It is the severs that take most of the "work" so they would have to update them so they can "talk" to the PS but that would not be that hard.

It can be done, on the PS side of things, so i am sure the new 720 can be worked the same way. PC for sure.