I think splatoons overall sales stand and fall with it's north american performance. It's Nintendos strongest overall territory but It's also the only territory where the game is full price. Nintendo must be confident about it's performance there, to go with such a wierd pricing pattern though.
I read a lot of comments around here by people who don't quite want to shell out full price for the game at launch, so that has me worried about it's NA performance. :/
I hope it does really well. Nintendo is certainly pushing it, and the demo did wonders, so that helps. But overall I'm sceptical that it will actually do that well.
T-bones optimisn is always appreciated though! ;)