It's been a long time since AP has had a good sale on Steam. Was $2 like... two (or more) years ago on a random midweek/weekend deal. Grabbed a Steam version when GMG had the sale. You never know, though. Unless you're dying to play it I'd just keep waiting.
Yeah, I just checked the sales history of it...it's only ever gotten down to as low as 5 bucks 3 times. But you're right, it's not a game I'm dying to play. Never know when it might drop again.