I think it is a combination of holding back ps3's for ffXIII and GOW3 release.
I have lots of friends who just seem to be waiting for gow3 or ffXIII to actually buy a ps3 and after that they will work their way backwards going through older games.
I think this year will be tough for Sony and keeping up with demand without hitting too many losses. At the time of MGS4 release, the ps3 was still expensive. Now we have a ps3 at a very competitive price and they are releasing 3 games which have the potential to push hardware; FFXIII, GOW3 and GT5.