Yes, it's due to the fact that the PS3 has a split CPU/GPU RAM memory of 256Mb/256Mb, while Xbox has one big RAM memory of 512Mb that both CPU and GPU use, which allows for more flexibility when a game is particulary heavy on the CPU or GPU, in Skyrim's case probarly the CPU.
To everyone explaining why PS3 may be more difficult to produce for, I completely understand your point and the truth in it. However as a PS3 player: their job is making video games.. I think I am not alone in wishing that they were actually capable of doing their job for all consoles, not just ignoring PS3 because "it's harder."
I bought a lamp ten years ago.
Its brighter, and more effecient than a torch I bought last year.
Should the torch I bought last year automatically be better as a lamp because its newer?
Thats what your argument boils down to. One console came out first, so the second console thats got very different hardware, should be totally better even though it was developed mostly at the same time as and completely seperatly by different companies with different aims.
The xbox360 is the lamp. The ps3 is the torch. Both of them give us light, but to read with the torch, I need to position the torch just right, or hold it over my book.
therefore its newer, but harder to work with.
... I rambled.