Keep in mind that MS was releasing games for the 360 a year before Sony started releasing games on the ps3, and that even once the ps3 was released, Sony was still heavily supporting its other two platforms, going so far as to release God of War II on the ps2.
For example, PD0 and PGR3 were hitting the 360 at a time when Shadow of the Colossus was hitting the ps2.
Now that Sony's first/second parties are more fully focused on the ps3 (well, 50/50 ps3/psp), things are beginning to pick up steam. This year and the tail end of last year are signs of that.
Also, I wouldn't consider Mass Effect to be a first party/second party title. The IP is owned fully by EA, and they can do with it what they please. MS may have locked up exclusivity for ME2 in addition to ME1, but that's no different than deals like Bioshock. Same goes for Tenchu Z and Project Sylpheed. In fact, Square published Project Sylpheed in Japan. Tenchu was published by From Software in japan as well.
And I suppose a case could be made for Gears as well, as MS doesn't own that IP, but I'd think they would've locked up a decent bit of control over the franchise.
Sony, however, owns and has full control over every IP attributed to them on that list.
