1. Newer tech is less tried and true - more bleeding edge
2. Both companies were caught in an "arms race" for better graphics
3. More complex internals
P.S. I had a PS3 break too.
GameCube and Xbox were a lot more advanced than the PS2, but had far fewer problems..... I would bet the only reason the Wii has more problems than GameCube is it is being produced a bejesus lot faster than any console before.
The PS3 is more "bleeding edge" than the X360 yet it has a much better track record for not failing.... admitedly there is at least one good reason why PS3 is much better than previous Sony consoles, and that is the less stretched production as they are not in so much demand like PS1/2 and Wii were/are.... but that can only account for so much, so the PS3 is obviously built quite well (I would have said very well had you asked 6 months ago)