For one, you can copyright a schematic but the copyright is on the schematic itself. To keep someone from building what the schematic describes or their own twist on it, you need a patent.
But the point of open x is that you don't want to keep someone from building what the schematic describes. Yes, there are "open source" licenses that tries to limit what you can do with the source, but the main point is always that you can take the source and improve upon it. That copyright is needed to enforce this is newspeak from the GPL camp.
Are you kidding? You can't have "licenses" for things you don't own. If the work doesn't have copyright protection, then its in the public domain. If you try to force me to obey some "license" I can simply choose to ignore your license and use the work anyway. Copyright is necessary to enforce the license, like say the GPL. Without that license, I can take your "open" software and do anything I want with it, including adding my own modifications to it and selling the entire thing without giving anyone any right to see the source or anything else. And you can't do anything to stop me legally. Since one of the primary principles of open source is the "share and share alike" principle where if you use it, you yourself have to contribute under similar license, that principle can only be enforced if you can enforce anything at all, and that requires legal protection. Copyright provides that protection.
The problem that Bruce has identified with Open hardware is that the only way to enforce anything with hardware requires patent protection analogous to the copyright protection that allows open software licenses to work, or extending copyright protections into new areas. But the problem is that both using patents in this way and trying to extend copyright protections instead of patents both seem to have legal gotchas that don't exist to the same extent with software. The problem is if the Open hardware movement tries to leverage either patent protections into designs or copyright protection into implementations it will either not work because the law won't evolve correctly, or worse they might evolve in such a way to allow Open hardware licenses to work but create a new form of legal ammunition that unscrupulous entities could use in entirely different ways to gain new IP protection rights they don't currently have.