To begin with, LBP is going to sell a LOT more than 1.5 million LTD.
LBP does not fit the PS3's audience.
Killzone 2 does fit the PS3's audience. CoD4 will easily cross 4 million, and you think those people are going to buy one shooter a year? No, they buy lots of shooters. If people see this advertised, they will see how amazing it looks, and they will forget about Killzone 1. Which, by the way, sold over 2 million units.
The reason Resistance 2 sold badly is because World at War was releasing at roughly the same time. The CoD audience are only going to buy one game at a time, and if it's between CoD5 and another shooter, they will choose the Call of Duty.
Killzone 2 launches in February. That is three months after CoD:WaW. The shooter fans will want another FPS. They will look for the best FPS on the PS3, and find Killzone 2.
That is why I predict 700k first week, 4-4.5 million LTD.