The two times I've been on an INTL flight with GoGo I was able to use a previously purchased day pass ($16, I think). My guess is that will also go away.
I guess the number of planes with satellite GoGo must be up to a point where they think people would pay monthly. It would piss me off to pay the monthly extra for global and then get a plane that didn't have it. It'd make more sense to pay the $40 when you got a plane with service and you needed it.