I don't really know what you mean by FFXIII, it was announced on Xbox just after it was announced on PS3, not after the PS3 version was released. As for whether or not it was 'gimped' then it's a good example, the answer is yes and no.
No in the traditional sense in that it was one of the few games to slip past Microsoft's ridiculous 1 disc policy, it was released on 3? discs, so all the content was able to be on both formats.
At the same, the fact that it was released on both systems meant that the dev team working on it had to take into account the weaknesses of both systems, rather than just concentrating on one. There is no doubt in my mind that had it been exclusive to either console, it would have been a stronger game.
There is a reason why exclusive titles are the strongest on those two systems, you think Xbox, you think Halo. You think Playstation, you think Uncharted. Those games aren't among the strongest due to idiotic fanboys, it's because they are tailored to the strengths of the systems they are on.