The reason why many 360 games don't render at 720p is due to the 10MB of eDRAM, its not enough if you wanna do 4xAA @ 720p, or FP16 HDR @ 720p, but if they drop the resolution to 640p it fits. Problem is scaling from 640p to 720p without any AA will cause severe jaggies, as seen by PGR3 and Halo 3.
As for PS3 games, it's probably lazy developers porting the game or finding an easier way to increase the framerate.
Btw GTHD is 1440x1080 upscaled to 1920x1080 OR native 1280x720 with 2xAA
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-------------------------------- Computer Specs ----------------------------------
Intel Pentium IV Prescott 3.0 HT → 4x 512MB DDR-DIMM → ASUS GF 6800 GT
Sound Blaster X-Fi → 2x Maxtor 80 GB (RAID 0)
Hitachi 19'' Monitor → Cambridge Soundworks Desktop Theater
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