It's not even an issue about PS3 vs Xbox although I know all the respective console fans want to make it one.
If you don't even bother to bring it up, it still boils down to fewer compelling exclusives that require you to own an Xbox (or PS3) when they are also available on PC.
It just so happens that there are more games being put out by SCE studios that never see the light of day on PC.
In either case, if you don't particularly care about whatever exclusives a given platform has, why bother even making it an issue unless it actually matters to you personally?