I simply think, like most others, that the Playstation has never been home to a few, big selling titles. Simple as that. Sony has tried to achieve this, but so far hasn't really.
Halo, Gears, etc. sell very well on 360, but if you look at the multiplatform games they either sell more or less evenly in ratio (i.e. more on 360 but in ratio to the install base difference), the same or even sometimes more on the PS3 (which is pretty interesting, when you think about it, as it means the attach rate, etc. is higher for those titles).
Really, when you look at it, a few key titles aside, games sell roughly the same on PS3/360 and sometimes skew to PS3. Those key titles on 360 are however huge sellers in a manner not commonly found on PS3.
I think I took a lot of words to say something simple, I hope it makes sense!
Try to be reasonable... its easier than you think...
