It's not just storing files as a service in some generic way. It's storing objects using exactly S3's API (or at least a subset) so e.g. programs and libraries written to use S3 can use DreamObjects instead by just changing the base URL. That's a clone of S3 as much as Linux was a clone of UNIX, and as much of a clone as there can be when the original is closed source.

Disclaimer: I'm on the GlusterFS team at Red Hat, which puts me pretty close to the Ceph team but not actually one of them. I've never had anything to do with Dreamhost.

What do you mean "no affiliation"? It's one of Dream host's services.