Why PS3 instead of XBOX360? With both consoles at parity with respect to gaming performance.
I don't think they are.
What factor of difference are you thinking PS3 has over XBOX360? I've stayed away from PS3 and XBOX360 centric magazines because of their respective biases. When you meet somewhere in the middle though, PS3 has been generally perceived by the development community as having a marginal performance edge, but a prohibitive development cycle.
Basically what I've gathered is Microsoft chose to have three symmetrical processors. You program them each the same. Sony/Toshiba's Cell is a bit more complicated in nature with having to keep the SPE's sorted.
Notably, John Carmack did say PS3 has a slight performance edge, but that Microsoft's development tools are top notch and it's a dream to program for. When I say the systems have parity, I am taking all of those things into consideration.
If you have this hoss system but you have to really get close to the internals to tweak it, and you are a game developer in today's market, you generally make the call to develop for both consoles. If you have time, optimization for each is a nice to have, but they are already nearly the same performance levels anyway. Both 3.2ghz procs. Both have similar memory bandwidths, with PS3 having something like 25MB/s vs XBOX's 24MB/s, I don't know if those are exact but I do remember looking and the bandwidth for bus and gfx were both within 1MB/s or so of each other.
Guess what I'm saying is it all comes out in the wash, hence my "parity in performance" comment. It's like coding in assembler vs. coding in C. If you get close to the processor internals, you will make it go faster. But is it worth it to game developers to lock into one platform like that these days? Video game market is highly competitive these days.
Look at Konami. They are releasing MGS on XBOX360. You ask them why, they flatly state because they won't recoup their development costs if they only sold on PS3. They understand what is up. And Virtua Fighter 5 is a time exclusive now instead of being a system exclusive like it used to be. It's coming to XBOX360. Sega understands the game now.
Sony used to have the GTA series as a system exclusive. That started to get chipped away when it became a time exclusive, you had to wait almost a year. Now they are simultaneously releaseing GTA4 for both consoles. Did you read that the episodic content, the extra missions you can download, that is an XBOX360 exclusive? I see the gaming experience starting to tip in favor of XBOX360. Sony will remain competitive, but most true gamers have known for a while now that XBOX360 with XBOXLive is the way to go. I've spent a lot of time on the 360 at my friend's house, you've probably spent a lot on it at your place as well.
Only thing I can think of that PS3 has over 360 is Gran Turismo. That's the one they won't come off of. And Forza Motorsport 2 is going to give GT4 a run for its money. That's why I keep coming back to "parity."
Now if you want Blu-Ray, that makes the case for a PS3. You get games AND HD movies all in the same kit. Great value proposition if you don't mind supporting the company that brought you Sony Rootkit. I'd rather wait for the HD video download services to scrap it out. The HD-DVD/Blu-Ray stagnation stalemate just shows me that downloads are the future. There will be a lot more competition in that arena instead of just two main competitors. Where there's competition, there's consumer advantage.