I wouldn't be smart at all.
Well i dont know all MC/VISA rules about fraud in US, but i can tell u - merchants frequently loose their money then they provide not enough security - even if we talk about virtual services in virtual games. There are lots of fines in payment system-bank-merchant agreements about fraud assistance(not preventing fraud).
And cmon - there is only one gamers in all active comunity that dont want to pay thru paypal. Ok 39$ in a year less.
Becoming merchant thru bank-acquire directly will cost them several thousands i guess

bad buisness