I couldn't care less what the cloud, or SAS, or software is running _on_. What I care about is whether or not it provides open, standards-based interoperability.
Does Amazon s3 run on linux or bsd or WIndows ? I don't know, but I do know that I can't just connect over plain old SFTP or WebDAV without major gimmickry and transformation. (FWIW, providers like rsync.net do, in fact, allow direct, standards based interaction, so it's not impossible).
On the other hand, another cloud-like provider might run on a completely closed source, proprietary foundation, but if it provides plain old standards based interaction from the outside, who cares ?