These things always go up and down, but to be fair B&W is an old game. I find it extremely impressive that it's gone this long. I think the winning part of the forumla is that it is a very open game allowing for people to let their imaginations run wild.
It's been fairly consistent in it's following for the last few years never really dropping that much, except for a while after B&W2's release, so I could see this game still going for a while more. The real classics never get old :yes .