Quaz who admits to only owning the Xbox 360 version of the game, speculates the PS3 version of GTA IV runs at 640p all from studying raw screenshot output sent to him from Dot50cal (another Beyond3D poster).
Well lay the rumors to rest not only considering Rockstar themselves confirmed both Xbox and PS3 versions to be running in native 720p back in previous issue of EGM during an interview when asked if GTA IV would be running 1080p native,
BUT, Gameradar also confirmed GTA IV to be running in 720p when they were able to capture raw-output video straight in 720p from both versions.
As some of you may know, it is also discussed in Beyond3D forum, raw output ensures the video does not get "up-scaled" and prevent's "post-processing" thus viewing the video in its truest natural form.
"We’ve played both console versions of GTA IV, and took the following video from the opening scene. We captured the raw video in uncompressed 720p, with no post-processing to either stream. Shown side-by-side, it’s quite difficult to tell the difference between the two versions. Only a highly trained eye can see the subtle shifts in color, the minor variations in shadow detail."
Now stop wasting time arguing about which version has better resolution and just enjoy the game!
look at where Kotaku's source was - Eurogamer, and who in turn got the info via Beyond3D Forum