Pretty good sales. The main obstacle for LBP I felt was the install base and demographic of PS3 plus the unkown factor of the UGC.
The PS3 has lost a big chunk of former PS2 demographic to Wii, who would have driven even more sales of the title I think, plus I'm sure the whole UGC put some off too.
Personally I think 3 million is pretty good, even allowing for lower price. Also, I'd be willing to bet that any losses on the lower price to get the title into homes was more than covered by the DLC. Everyone I know with LBP has spent plenty on top with DLC for costumers, packs and the like.
Try to be reasonable... its easier than you think...