I think it can be said that PS3 gamers differ a bit from 360 gamers in their approach to buying new releases. I think 360 gamers are more likely to go into a GameStop and pre-order upcoming titles, while PS3 gamers kind of buy them when they want them. I've noticed on the sales charts that the 360 version will start out higher but will often fall below the PS3 version in subsequent weeks (excepting shooters).
I wonder if perhaps this has something to do with the average 360 gamer being more focused on competitive online play? I don't know, but I think it would be an interesting trend to track.
Also, it breaks my heart that Valkyria Chronicles isn't higher.