Because the PS3 version is a bit poopy.
This.
I played RDR on Xbox360 two times through, then later the PS3 version to 100% completion. I can guarantee you that the PS3 version is weaker.
There's a weird pause bug when opening containers - Marston just stands there with the camera above his shoulder, until usually pressing Circle forces him to move. Also another pause bug during poker occasionally. I also think the graphics are not as good - in the rain it seems more noticeable.
But the biggest pain is the
animal spawning bug. There are several areas where animals constantly spawn and it seems like skinning them may cause them to spawn. Where you exit the Tall Trees area on the way to Beecher's Hope and just south of Fort Mercer where the mountain lion spawns at a cross road ore just two of those areas. There are a couple more bear areas.
I've been trapped in bear spawn hell where I can't leave because they keep spawning two at a time while I'm skinning one. I can stand in one place and look around me and see the dead bodies and nothing else. I get into the skinning animation and you can fucking see them pop up in the background and kill your horse during the third stab.
Really sucks because after my fourth RROD I threw my 360 away and gave RDR:GOTY away to a friend and bought a PS3 with that version of GOTY edition and now I wish I had the Xbox again.