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.

It has been promoted on the front page of iTunes, of course. But how did it get there so quickly, and why do handhelds only feel complete when they’ve got that one puzzle game that fits them – the GameBoy’s Tetris, the PSP’s Lumines, the DS’s Slitherlink?

Partly, I think, it’s because puzzle games are systemic: they don’t end, just as going on car journeys and pulling out the old GameBoy doesn’t end. They’re ruminative, and they fit the ruminative nature you can get into with a portable console or mobile phone. Then there’s the fact that handhelds often end up being held in the hands of a different kind of audience to the Gears and Halo crowd: they seem less threatening, less aggressive. They’re also a little more stylish, and more universal: they leverage the brand value of numbers and letters and shapes rather than the brand values of Marcus Fenix or Lara Croft.

There’s possibly something in all of this, but I’m nowhere near the bottom of it – just as I’m nowhere near working out how Puzzlejuice hit the mainstream so very quickly.