Yes but real hardware with an SSD disk plugged inside could deliver excellent performances with many reasonable on-disk databases, with a fraction of the cost per megabyte, with many many millions of keys.

It is like that other than the fact you don't have to manage the DB, that is a good point, here the best reason for many small-mid business to use such a service is since they are already on EC2. May work in the short term but I see something odd about this model.