Sweeny makes some good points, I also have stated before that I don't think we'd see another gen of consoles until beyond 2010.
In all honesty the XBox 360 has alot of advantages over the PS3, it's easier to develop for a start. That's not related to the hardware, the 360 Dev Kit, is very similar to working on the PC, you debug in VC++ etc... It's pretty much the same process. Working with the PS3 SDK, while not hard, its a different experience.
The PS3 suffers from the fact it basically has a Geforce 7 card bolted into it, the CELL processor operates in little endian, and the GPU in big endian (I could have those the wrong way round) this means an endian swap takes place.
The CELL has alot of raw processing power, but it's not like your PC, it's not like you have 7 PC processors, you actually only have a single processor which is like the PC, and that's the PPU, the rest are SPU which have some memory limitations, etc...
When we compare it to the 360, we find the 360 has an equally powerful GPU (infact some would argue more powerful), you don't have to do an endian swap, and it has a shared memory resource, PS3 has dedicated video and system memory.
The 360 is more like a triple cored PC (it's not exactly like it mind).
Developers actually seem to be having an easier time with the 360 opposed to the PS3, and the strange thing for me personally is that basically, of the multiplatform releases the PS3 always looks and plays the worst.
So what am I getting at? Simple, the PS3 is actually no better as a games machine than a 360, so why buy one?