My suspicion is that Microsoft and Amazon aren't interested in charging in here because they're much more in "frenemy" positions with Apple; Amazon used to be f

My suspicion is that Microsoft and Amazon aren't interested in charging in here because they're much more in "frenemy" positions with Apple; Amazon used to be fairly antagonistic toward the Big Fruit, but they've been more amenable to having their various services work together gracefully over the last few years, and Microsoft has ended up being pretty enthusiastic about Office on iOS. So they probably just figure that it's not worth going to war over.