Wipeout HD for example runs most of the time at 1920x1080 60fps. The engine is clever enough to drop that resolution down on any frames that need it in order to maintain 60fps to ensure smooth gameplay. Apparently the majority of the time you are in true 1080p.
You just said that Wipeout HD needs to change resolutions on the fly to maintain playability. So you just said that the PS3 aint powerful enough to drive 1080p @ 60hz. I'm sure it can drive 1080p @ 30 or 24hz.