LBP was huge... I don't see how 500k in one week isn't huge. Since when is selling half a million in a week not good. Remember the majority of games out there sell less than 200k in their lifetime so being able to do 500,000 in one week is pretty damn good.
Of course you can compare it to games that do over a million in their first week and it doesn't look as huge, but I find that silly.
I think any game that is able to outsell the majority of it's games in the first week is a pretty huge title... and I'm sure the developers feel the same way.