It's Top #15 (checked moments ago) and has been 12, how is that low? It's also competing against a bunch of ridiculously popular stuff like the new Sid Meier titles, the ever-selling CS:GO, Football Manager and other "macho" stuff like Lord of the Fallen (someone please find a way to change the capsule art, that cover is a crime against nature, bald angry dude and all, to think they even had the never of putting a bloody statue of the guy as a collectible, lol), I would say it's doing pretty damn well. Hell, it's quite way above DayZ, another Steam darling.
I also take that sales through other outlets (like GMG) don't count to the Top Sellers within Steam, right? (I bought it on Steam because I had Steam Wallet cash left, heh.)
Anyway, need to get that hype tank rolling, GAF!