I don't have the answer to this, by the way, but I do think it's interesting. The reason I'm asking is that, as I write, Puzzlejuice, Asher Vollmer's brilliant blend of Tetris, Bejeweled and Boggle, is right behind Pajitnov's hardy perrenial in the iPad app charts. It's been out a little less than a week and has had no marketing by the developer.
There are some games that you just know came about because someone down the pub said, "hey wouldn't it be great to combine [incredibly successful game X] with [equally successful but slightly different game Y]!?" And then, instead of going home, falling asleep on the sofa and forgetting all about it, they actually sat at their computer and wrote it. PuzzleJuice is one of those games.
But, wait, damn, that's not a bad thing.
Over at its IGF listing, designer Asher Vollmer describes Puzzlejuice as, "a game that will punch your brain in the face." That doesn't sound very nice, Asher. Luckily, Puzzlejuice looks a lot more pleasant than that.