Yeah, exactly what Occham said.

It's actually even simpler than that. If we make the in-game currency some arbitrary thing (like gold in other MMOs, we went with Credits for the sci-fi theme), then we can easily have you buy a pack on Steam. We don't ever even see your credit card. No need to ever charge our customers directly.

Our thought was to take it up a notch and use Bitcoin as the actual in-game currency. But that would be akin to associating a credit-card with each account, and having the in-game currency be the balance on that credit card. Then our in-game currency is essentially the USD, Euro, or whatever the player is using. This would be a nightmare. Just the exchange from one fiat to another would be huge. Bitcoin theoretically solves all those problems, which is why we considered it. Plus it's just cool as shit to do something like that.

But securing everyone's wallets is just not something we can handle.