KZ2 problem with sales has nothing to do with the merits of the game itself. Literally outside of MGS4, GT5P and GTA4, no game has shown phenomenal sales on the PS3 in the US.
All you have to do is look at NPD through the years of the current gen and see PS3 sales aren't all that impressive. Outside of GTA, the PS3 has never had a 7 figure NPD sales month for any full fledge title. Outside of maybe COD4, the PS3 has never posted a 600K month of sales of a full fledge title during Nov and Dec. Looking at NPD over the last two plus years shows that the Sony's problem with US game sales is systemic and the problem lies with the types of gamers the PS3 generally attracts.
Which IMO falls in 3 categories:
PS3 Blu Ray only
Dual owner
PS3 single console owner.