Bethesda has said that the PS3 has issues for their game. Honestly I think it's because they are incompetent. There's plenty of large scale games on the PS3 that don't have all these problems. They want to push blame aside instead of retooling their engine for the PS3. Supposedly they are close to having most stuff fixed, but nobody really knows.
I guess since the Xbox is closer to a standard PC in terms of specs it's easier to work between PC and XBox (mostly xbox) but then they try to port to PS3 and they broke some stuff in the engine during the process. One of the major issues has been Save file bloat. The save file balloons to huge sizes and it causes freezes due to all the stuff the game is keeping track of. This happens on PC too. Supposedly the game saves the cell state (area state) where it keeps track of all the items you drop, dead bodies that won't disappear immediately, arrows left over from battles etc. This will reset after so much time and I've heard of different methods and times for this reset. Some people say wait 3 days, some people say sleep 3 days, some people say it takes 30 days game time. I honestly don't know.