Not sure this is the right forum to ask the question. Seems like a high adoption of these games here. The question is why other PS3 owners aren't buying these titles. If no-one has bought them, great, we can benefit from their reasons. However, we really need to find some people we know haven't got 'em and ask them why!
Well, I'm not sure about this, so it's just a guess on my part.
But if I see really hyped up games like AC and CoD4, which got quite some advertising too here both going for 59.99 and 64.99 euro's, and next to it, I see a fairly unknown game (new IP) like Uncharted, without much hype, nor advertising, for 74.99, I think the choice for many people is made here.
(These are Belgian prices btw, don't know anything about pricing in other countries)
It's just a guess though, but pricing is imo still a big factor.