$5 each platform? (Score 2, Informative)

Poking around the checkouts I see that you buy the game individually for each operating system as opposed to buy once, run anywhere. If my main mac dies (again) I'll have to shell out again to play it on a Windows or Linux machine. Not a huge fan of this sort of arrangement, I liked Braid where I've paid for it once and have access to Windows and OSX copies.