Going in to more detail, I would analyze the situation in this manner: in terms of sales, the Wii has extremely strong first party support but weak third party support; the 360 has extremely weak first party support (this is Japan, Halo and Gears are anathema) but quite disproportionately large third party support; and the PS3 has recieved mediocre first party support with some sporadic blockbuster exclusive third party support, but very little AA or A support to flesh out the library in between those releases.
The result is a bizarrely fissured market where the only safe bet is the DS -- but I think some parties are very hesitant to put their important games on the DS because they're afraid of losing "mindshare," particularly amongst Western Gamers. Consider if Metal Gear Solid had been for the DS, for example. Dragon Quest is one of the few major games that can afford to be on the DS because it's already an ignored brand in the West.
It's really a very dangerous market place, and I entirely blame third parties for creating it.