While I do think that is certainly one of the more likely reasons it's another case of educated guesswork - this isn't a criticism aimed at you, but at the developers for their lack of forthrightness on the issue.
Previous CoD games are now hacked to pieces on PS3 thanks both to the jailbreaking and IW/Treyarch's over-reliance on Sony's console to provide security. I think it's a little late to start using that as an excuse to not give us an install. They'll simply have to raise their game as they had to with the Xbox console, aye?
