Microsoft pays a lot of money to get the DLC on the 360 before Sony does.
This, it's called a 'timed exclusive' and it's something Microsoft are notorious for, they pay a LOT of money to delay the release of DLC on other consoles (read: the PS3).
As for other issues, it's likely due to the fact it was coded for the xbox then transferred to the PS3, that's because the xbox has not changed much, it's highly similar to the original xbox and so coders know what they're doing, the PS3 however is pretty uncharted, or at least was when F3 was released.
I doubt there will be the same problem, though the DLC may still be an issue if MS want it to be. They're more used to coding with the PS3 now, in fact apparently they prefer it to the xbox...
Basically, don't worry. PC is still better than both