"Downtime that is their fault" is kind of a giant caveat, no? Is it their fault if they lose transit or power, for instance? With that level of refunds I suspect "their fault" basically only covers one of them accidentally running over a server with their car. The problem is, that guaranty isn't getting anyone anything of value.

I suspect Heroku has SLAs for their bigger customers, but don't really know for sure. I do think you're overestimating what kind of incentive an SLA is for a provider, though. SLAs are basically an on paper way of showing your commitment to keeping things running and responding to problems. If you don't have that commitment already, the paper isn't going to change anything.

Pointy haired bosses and lawyers love SLAs, but smart people who shop for this stuff don't care all that much about them. An SLA isn't going to convince me to go with one provider over another, nor is lack of an SLA going to make me avoid a provider I already like and respect.