Other than simply offering a reason to get a PS3 rather than a 360, the more first party games there are, the better, as they are the best games (on average) as the Sony first party devs (and Insomniac) seem to be able to get the most out of the system, although exclusives are
Personally, there are plenty of 1st party games coming, it's just a matter of when. GT 5 is coming, and should be here by the end of the year, but it is still a should, not definite. MGS 4, although it should make April, has been delayed for a long time. Naughty Dog wont get anything out till 09, Insomniac will get something out. MS 2 is coming, and we should see more DLC for Warhawk next year. There is also inFamous next year, LBP, but there are rumours that it has been delayed until the end of the year. WipEout HD is being made but that is not a major release, just a downloadable game (as far as I know). GoW 3 will not come out till 09. There is also the Getaway and 8 days to Vegas coming but nobody knows when or anything about them apart from the obvious (the Getaway is in London and 8 days to Vegas is about going to Vegas I think).
Sony's main problem is delays