You are right, the manual says:
Note: As of PHP 4.3.0, both source and dest may be URLs if the "fopen wrappers" have been enabled. See fopen() for more details. If dest is a URL, the copy operation may fail if the wrapper does not support overwriting of existing files.
I guess last time I had checked it was still in pre-4.3.0 era because I distinctively remember having tried this...
I will immediately get to work and see if I manage to make it work.