But the majority of people don't need that much HSM. And that's the interesting problem I see with this: the enterprise can afford it, but is going to be wary of using a cloud provider for this sensitive of data; and it's outside the budget of most startups. There is probably a tier in the middle, though, that Amazon expects will happily use the product.

If you're using an HSM for full DAR of your servers, you need all the H/A you can get. IF that HSM is down, you can't boot your systems, period. If that HSM crashes or is destroyed, you potentially lose everything.