Multiplatform titles tend to have deeper userbase penetration on the PS3 versus the 360.
I think its really comes down to the demographic difference between the two userbases. I think the PS3 userbase is more strongly populated with gamers who used to be part of the core gaming crowd in previous gens but are more casual in their gaming habits this gen. A population of users where gaming isn't as an attractive hobby as it once were in years past.
Looking at that list, its dominated by the PS3 but look at the games that have higher penetration on the 360. Out of the 30 or so data points, the xbox only shows higher penetration 9 times. Of those 9 times, other than the COD franchise, the 360 list is populated by franchises exclusive to this gen (Bioshock 2, Borderlands, Prototype, Army of 2 and UFC). While the PS3 shows higher penetration of the other 20 or so data points, new franchises only account for 2 of those data points (Rockband and Batman AA).
Look at the first party and exclusive titles on the PS3. They are mostly dominated by newer franchises but haven't performed to the level seen on the new exclusive franchises on the 360. Yet exclusive titles like GT5and MGS4 haven't had a problem with sales. PS3 show greater uptake rates with multiplatform titles because multiplatform offerings are indundated with franchises that stretch back to the PS2 and beyond.
The PS3 crowd isn't as interested in being as involved in gaming as in years before and thereby tend to gravtitate to franchises that they know from their past gaming days.
I also think that PS3 crowd is more interested in multiplatform because PS3 mp titles also benefit from the noise generated by their 360 fans. Multiplats are more likely to be indirectly marketed to those who don't keep up with gaming as they did previously. Its not like your 360 only friends are going to make you salivate over UC2 like they would COD, Madden, GTA4 or AC. Who talks about a franchise thats not on their system?
