As I understand it, those guarantees don't mean that the service will actually stay up for the given number of 9s; it's that you'll be reimbursed monetarily if and when they go down.
Kinda the same thing, though. I mean, from my perspective there's no substantive difference between me saying "this service will stay up 99.xx% of the time and me buying insurance to pay you for the 0.xx% of the time I might fail.
The alternative is that I use the insurance to pay my legal fees when you sue me for not meeting my uptime guarantees.
It's not the same thing. The Amazon service might only be costing you $100/mo, but if it goes down the cost to your business might be millions. They'll reimburse you the $100, not the millions.
