We've found AWS has a richer ecosystem for the things we want to use, e.g. We're using PostgreSQL RDS for our managed RDBMS.
It's also nice to be able to point your deployments to any server instead of being coupled to Cloud-specfic tooling. i.e. If Cloud costs ever get out of hand we can point to the better value and performing dedicated hosts like hetzner, with minimal migration effort.
I assume you could just deploy to an Azure/Rackspace/Other VM or to a physical server rather than an AWS VM if you decided to, there's nothing PAAS specific here. Is that correct?
It's also nice to be able to point your deployments to any server instead of being coupled to Cloud-specfic tooling. i.e. If Cloud costs ever get out of hand we can point to the better value and performing dedicated hosts like hetzner, with minimal migration effort.