Two things about this graph...
1) It is misleading. This graph pits Xbox 360 and PS3 side-by-side with no mention of PC games, and then goes on to omit a number of games (at least on the Xbox side), presumably because PC versions became available later on. I'm noticing Fable 3 and Alan Wake right now, and there may be others, on either side. In a console vs. console comparison, Microsoft's offerings are more robust than this graph is indicating.
2) Even when we add console exclusives to the Xbox side, there are still clearly more controller-based exclusives on the PS3 side, and many of them are unquestionably high quality games. So why have I not switched over to PS3 as my main console? Because there are a couple of issues that a large quantity of games is not able to solve:
a) Money. Just because Sony puts out more 1st party games doesn't mean I have the money to buy them all, AND still buy the 3rd-party games that I want. Sometimes a 3rd-party game will take priority for me over any 1st-party game that is available at the time. At the end of the day, I wouldn't be buying any more 1st-party games if I were a PS3 owner.
b) Appeal of the games. Many of Sony's high-quality games simply don't appeal to me, or else don't have as strong an appeal as some of Microsoft's games. Out of all those controller-based games on the Sony side, only about 4 or so are games I'd actually be interested in buying (Uncharted 3, The Last of Us, LittleBigPlanet 2, Heavy Rain), and I'd still rather have Halo: Reach and Halo 4 than any of those four PS3 exclusives. And it's not just Halo; Fable 3 and Alan Wake appeal to me more than God of War 3, even though God of War has more impressive visuals and got a better Metacritic score.
