A licensee could avoid the GPLv3 patent restrictions on software licensed "GPLv2 or later," for example, by choosing to stick with the GPLv2.
... unless he want to use a newer version of the software which RMS has decided should be licensed under the GPLv3 only. FreeBSD has run into this problem with gcc, for example: We could no longer backport bug fixes, but instead had to "clean-room" re-develop them.
Right, I'm saying that's intentional on the part of the FSF, and an "any later version" clause doesn't let them do that. Obviously, that's not helpful for you, but if that's what they're trying to do, they need to be able to relicense in order to do it, which means either copyright assignment or agreement from the copyright holders.