LBP2's performance is not surprising at all to me. LBP is meant for the creative people amongst us, and the ones that enjoy playing games made by other people. I found out I'm horrible at the creative part and I can't be arsed to play shit made by someone else.
It will only reach LBP's sales when it's packed in (I bought LBP because of that), but without it will fail to crack 2.5 million in the end.