> Dropbox can operate in a similar fashion, re-packaging and reselling Amazon's services.
Yes, they can, and apparently have, but they're getting to the size now that they can achieve some significant economies of scale by building out their own storage infrastructure. Their profit margin has to be pretty low with S3.
"You can't be a storage company without having your own storage solution in backend."
I am not sure that is necessarily true. There are plenty of web hosting resellers who are successful without ever buying a single server or a single line. They've repackaged and re-sold a service. Dropbox can operate in a similar fashion, re-packaging and reselling Amazon's services.