Yep, PS3 is more powerful. However, no developer has successfully actually taken advantage of this, due to the fact that the PS3 is very difficult to program for. Sony has been criticized extensively for this.
Also, the engine that SE is using for FFXIII allows builds for PC/360/PS3. This means, that for the most part, regardless of which system you develop for, the output will be the same. There will be minor differences for QA to hammer out like usual, but generally it doesn't matter which system they start development on.
XI Wiki


