They originally announced FFXIII as PS3 only as well and I figured I had to save money to get a PS3. But low and behold... it came out on the 360 and I'm sure they would consider it a "success".
Hopefully Versus XIII will be out on the 360. If not, then no big deal. I know I only speak for myself since I still have the PS3 money saved. It would be nice if they did away with the exclusives though. Release it for all the consoles, get more sales out of it.
I heard from a friend, that S-E wanted to release the upcoming FFs to be multi-console. And there are even rumors that FF15 will be released on the PC. But they're rumors, so no 100% guarantee ofcourse.