Firstly if you haven't seen an XBox360 disassembled then you should have a look Here First.
Some Japanese folks took it upon themselves to quickly disassemble a PS3 and post the video on YouTube:
Part1
Part2
Part3
Part4
From watching these something becomes very obvious. The PS3 is a very difficult console to put together. There are a few silver cables that look like they need to be connected by hand and the whole thing has so many parts that it looks like production must take many hands.
Obviously the 120mm fan is why it cools so efficiently and quietly, it is a shame that the 360 doesn't have one too, but when you look at the 360's design you can clearly see that it has been designed for mass production with the arrangement seems to require little more than the motherboard to be fitted and it's case to be screwed on.
Sony said the PS3 was a complex system and that was an understatement.