I know why, because, if you look at Metal Gear Solid 4 in Japan, it hasn't even sold a million yet because only 2.38 million have bought the PS3 there, if more had it then the sales spike for MGS4 would have lasted at least a week longer, in USA, just over 5 million people have bought the ps3 so the sales spike for MGS4 lasted a week.
This means that if more people had the PS3, the sales of really good games would continue like with the Wii, for instance, Mario Kart Wii, Wii Play, these games have each sold over 5 million because there are more Wii's out there, and are still in the top 10.
Lets hope that the LBP sales will always be big, and PS3 sales become like Wii's forever
DS: 120,000,000; Wii: 60,000,000; Xbox 360: 38,000,000; PlayStation 3: 34,000,000; PlayStation Portable: 60,000,000
PLAYSTATION®3 is the future.....NOW.......B_E_L_I_E_V_E