two things you also have to consider is that most games released with a much smaller ps3 userbase which means many times, ps3 owners bought the console after the release of those games so they could only buy the games months or years after release.
games which release nowadays have a much bigger userbase to sell to at release and probably much less will buy a console after this games releases.
as example heavenly sword released with maybe 9 million ps3s, now we have almost 70 million.
then you use a game like motorstorm which was a start title of the console which means first week sales are only for japan and not for the whole world. that would put motorstorm above 200k and not to 17k, same with resistance, first week of resistance in europe was 144k. or heavy rain which sold 400k+ fw in europe+usa, you have it as 25k.