Yet another user asked Sawyer if these problems are exclusive to PlayStation 3, which he answered, "as with Fallout 3 and Skyrim, the problems are most pronounced on the PS3 because the PS3 has a divided memory pool." When pressed on what a "divided memory pool" means, Sawyer clarified: "The Xbox 360 has a unified memory pool: 512 megs of RAM usable as system memory or graphics memory. The PS3 has a divided memory pool: 256 megs for system, 256 for graphics. It's the same total amount of memory, but not as flexible for a developer to make use of."
Also, that article was taken entirely from: http://www.gamesas.com/index.php?/topic/1303536-new-vegas-developer-comments-on-ps3-lag-issues/
So we can probably continue the discussion there, or ya know, the topic this came from.