[sliverstorm]

Steam doesn't allow in-app purchases that circumvent their distribution system, and that's a load of crap.

The idea there is probably something along the lines of preventing developers from selling their game for $0.99 and "unlocking" it in-app for $59.00.

[theevocater]

steam isn't an open 'app store' though. It is entirely curated through valve. Valve chooses the games to list and if they aren't happy, they will not ask you to list with them. They could easily refuse to sell games if you did that.