The OP's point:

Either you are reliable or not.

If you claim that the data is backed up and so on, then you are giving a garantee. Now yes, if all of amazon's datacenters burn down, or the one where ur data is, yes it will be lost, but that should be the corner case that you prepare for. Thats when you do an offsite backup in your house daily/weekly to ensure that at least there is no one place that burns down = company down the tube.

No matter the solution there is always the probability that shit will happen to all of it.

However if you are selling a reliable service, don't sell an unreliable reliable service. Reliable should mean that at least you back it up so that if one hard drive rack blows up, the data is not gone.