I just looked at the charts: the release of the original Halo 3 made XB360 WW sales reach 228k from 164k the week before.
It was the end of September 2007, shortly after, at the beginning of December 2007, PS3 started outselling XB360 almost continuously until the end of July 2008. PS3 outsold it another 2 weeks in August, with MGS4, IIRC, then with September 2008 price cut XB360 started outselling PS3 almost continuously until September 2009 price cut for both, when it started happening what we are seeing.
So Halo 3 moved 64k WW first week, a 39% increase, it's quite difficult that ODST achieve the same result, but thanks to Wii cut announced for the week after, it could at least outsell it.
Stwike him, Centuwion. Stwike him vewy wuffly! (Pontius Pilate, "Life of Brian")
A fart without stink is like a sky without stars.
TGS, Third Grade Shooter: brand new genre invented by Kevin Butler exclusively for Natal WiiToo Kinect. PEW! PEW-PEW-PEW!