Authorship Attribution is not a major concern for the GNU GPL. The GPL enforces source code availability, it protects the source code, not the author.
If you want attribution, you should have picked the Artistic license, or one of the academic licenses, like the BSDL.
While the copyright notice is negligible in some contries, most copyright laws have an enforcement that any such notices must not be removed. The redistributer is not required to advertise the original authorship, but stripping it out is not generally accepted either. Depends on where the redistributor lives. So you can go there, whatever the GNU GPL says. (It doesn’t care, however.)
Another note: If the plugin redistributors intentionally trick blog owners to provide commision to the plugin “stealers”, then you should also report that to Amazon. I’d guess they can look into that, any maybe freeze the account. That sounds like deceit. And there is surely a provision for that in any revenue contracts.
