I get your point, but why does Apple then stack photos and mp3s?
its the old PARC UI/UX concept..ever see a Lisa Apple computer JC? I know you have seen at least one right? It borrowed some concepts from PARC and that was one of them..
to me even creating proprietary client and apis for synching files and folders seems like making things needlessly complicated, when you can use rsync ad sftp (and fuse and sshfs) all of which rely on rock solid open standards.
but I understand that Dropbox became so popular because it made files and folders synching accessible to everyone who could already use files and folders. as simple as that.
in this perspective Receivd (I too think that the name sucks) could be a winner