Well, you see, if you sign up here as a new member and select your user name, it immediately tells you that you can't have a name if someone already has it. At least I assume it does, as I haven't actually tried it since the new software was put online, but nevertheless, that shows the functionality is already there.
Unless it's a matter of maybe the marketplace software just works differently? That I could see.
However, FWIW, I think that functionality should have been included from the beginning.
Why would y'all have not considered such a thing that would seem to be so obvious?