Often it's nice to just have conventions and gentleman's agreements. But then sometimes someone doesn't and the harm is done, it's too hard to reverse.
NFS has introduced the de-facto standard of using <host>:<path> for the device of a remote mount. Yes this break because you can have ":" in a filename, but in practice it works.
But somehow cifs (formerly smbfs), decided that adhering to the windows syntax was more important then adhering to the unix standard, never mind that it's a filesystem implementation for unix-like systems. So the remote mountpoint for a cifs filesystem is //<host>/<path>. Yes, this breaks too, you could start any path with "//". But it's just plain annoying when trying to figure out if a filesystem is remote or not.