Well its a question of balance.If you display at 1080p you need way more processing power to do the business...some developers just stick with 720p(or even 680p) to keep a better balance between frame rate and effects and resolution.
On the other hand ,it has been very expensive and hard to develop tools for making HD content at 720p ...imagine with 1080p they just have to rework their graphics libraries etc.Not a very big deal but given the deadlines its better to go with 720p.
There are quite a number of 1080p games on the PS3 in any case.Just by memory I can cite Lair ,Ridge Racer 7 ,Virtua Tennis 3 ,Marvel Ultimate Alliance ,Wipeout HD and Gran Turismo 5 Prologue...plus some stuff of the store as Flow ,Super Stardust HD and the likes.Incoming we have White Knight Story ,Killzone 2 and I have some doubts with Resistance 2 wich I have seen some mags saying it was 1080p.
Other thing is the upscaling thing.At first PS3 games didnt upscale at all.Later it was revealed a scaler chip on the machine that combined with some software solutions started to make some games upscale to 1080i and 1080p.Thats what the 360 does when it puts 1080p in its game boxes ...they are really 720p native but upscaled to 1080p.Sony usually gives you the upscaling to 1080i and leaves the upscaling to 1080p to the TV as all the Full HD panels do that anyway.Its bad for PR and message board trolling ,but the more efficient solution.







