I have played through the PS3 demo twice now and look better than those screenshots.
In all honesty the graphics in both versions of the game are almost the same -- the main differences between Bioshock PS3 and Bioshock 360(+ DLC) is the 4th difficulty level and challenge rooms...
In the end if you don't own bioshock on 360 or PC -- buy it for PS3. But if you already own than game than no, its not worth buying if you already own it on another platform.