I've only been skimming this discussion, but there seems to me to be a way to see a contradiction, but a way to see a resolution. Since you two seem to be talking past each other, I'll put in my $0.02.

Seeing how other people see it is always good.
1) The GPL says, as I understand it, that one cannot take a GPLed program and impose any more restrictions on it than already exist when the code is released by the original authors (unless all previous copyright holders agree). Or as [link|http://www.gnu.org/copyleft/gpl.html|it says]:

It doesn't exactly say that, though it says something similar. We've been arguing about the implications of those terms.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.

We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.

This is from the preamble. It documents the general intent of the GPL. It does not document the exact terms though.

The intent only matters if there is a lack of clarity in the exact terms that needs to be resolved. Therefore what you really need to examine is the section from where it says, The precise terms and conditions for copying, distribution and modification follow. to END OF TERMS AND CONDITIONS.
2) If GPLed code is licensed under "GPL v2 or later version" then the GPL [link|http://www.gnu.org/copyleft/gpl.html|says], briefly:

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

If you have followed the instructions of the GPL v2, this is indeed what it says.
Thus, the question becomes: Can a hypothetical GPL version 3 that imposes new requirements on the release of source code for "web services" be compatible with a "GPL v2 or later" license? Given what we've discussed here earlier ("closing the web service loophole"), and given the quote from section 1 above, and my limited understanding, it would seem not.

There is no question on this point, everyone is agreed. A useful GPL v3 is meant to address some issue with the GPL v2, and is likely to impose incompatible restrictions. Not just on web services, but there is also the suggestion of some terms that are meant to discourage the use of patents against free software.
I think that's what Ubernostrum has been trying to say.

Actually it isn't. What he's trying to say is that if the GPL v2 conflicts with the GPL v3, then anyone modifying a GPL v2 or later program following the restrictions of the GPL v2 must license their changes GPL v2 only.

In other words, the GPL v2 forces one to go from GPL v2 or later to GPL v2 only.
Perhaps the problem is in the understanding of what rights are granted by the license. "GPL v2 or later" doesn't give the user to do anything they want with the code. The user has rights to the code under the license, and the license is subject to change. Thus, one can look at it as: As long as the code is released under "GPL v2 or later" then the FSF can change the subsequent licenses any way they want and it will be by definition GPL compatible. As long as the code has a GPL "or later" license, then a subsequent GPL license could say that all code released has to have the [link|http://www.ntk.net/ballmer/mirrors.html|DanceMonkeyBoy] MPEG included and it wouldn't affect the validity of the earlier "or later" license.

Maybe that's what Ben is saying.

That is indeed what I'm saying. More specifically, I'm saying that because of that, the GPL v2 cannot force you to have to switch from GPL v2 or later to GPL v2 only.
I recognize that Stallman and Moglen have thought about these issues for years and are aware of the arguments about how many licenses can dance on the head of a pin. I'm sure they will craft a GPL v3 that is compatible with "GPL v2 or later" and clearly explain how.

I made that point as well. To deafening silence.
So it seems like the problem is going to be in code released under a specific version of the GPL.

We're in agreement on that.
[link|http://www.theregister.com/2005/08/11/gpl_fsf/|The Reg]:

On web services, Moglen said GPL required a "single legal phrase" that satisfied companies with different definitions of what it means to run software in the kinds of distributed environments that are the bedrock of web services.

I am very interested in what this phrase might be...
My $0.02.

Carry on. :-)

Thank you for the permission. :-)

Cheers,
Ben