People who said LBP might not break 2 million after the first 1-2 weeks of sales were fools. It opened much larger than Uncharted, and currently has similar legs, going by this weeks European sales.
If any game will have legs, it's a game like this one, and I wouldn't be surprised if it had better legs than Uncharted over time.
A few weeks ago i was predicting 3-4 million in sales for this title, with 5 million a possibility (and extremely optimistic possibility, lol), and it looks like it could break 3 million over time.