A couple of people have pointed out something that is important about the GPL2 "or later" license: the distributor chooses the license version they distribute under. (Actually the busybox maintainer Rob Landley pointed it out last week too). The actual language used on sources licensed as GPL2 "or later" looks like this:
* 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.
Note that this text uses "you" and "your" to apply equally to everyone who gets distributed to and who is distributing.
In the "distributor chooses" reading of this text:
* 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.
a new class of information is generated about the distribution action which I did not see expressed anywhere so far, that is a sort of distribution action license versioning metadata. For example if Nokia have a GPL 2 "or later" package on a secure (crypto-locked) phone platform, in the "distributor chooses license version" reading when distributing they can specify "Nokia gives you this specifically under the GPL2, so no keys". If the guy then distributes the package on, he can choose the terms afresh, but since he has no keys for the Nokia platform that has no impact on Nokia.
The distributor cannot make a GPL V2 "or later" distribution action stick when he gives it out under, say, GPL V3. If he says, here, have this GPL V2 "or later" package under GPL V3 only terms, the recipient need only redistribute it to himself or through a friend to have it validly on GPL V2 terms again. So it seems this distribution action license choice is only useful for one thing, getting the distributor out of distribution conditions found in later license versions, it seems it can't be used as a forced upgrade off older license versions.
Simply by stressing 'modify' rather than 'distribute' from the and/or:
* 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.
the text can equally be read another very different way, which is that the distributed-to person is granted the right to modify the sources "under the terms of" the GPL version he chooses. Someone who makes this reading of the text can believe they had a right to apply for example GPL v3 duties on their distributor, and ask them for the keys needed to allow installation as specified by the current GPL3 draft[1]. Folks can argue the distributor saying (where? when subsequently challenged?) that he distributed on the terms of GPL v2 beats out this reading, but it's not that clear to me because it was also the distributor himself that gave the recipient the license telling him he had the right to modify and distribute according to the terms in GPL V2 "or later"; if modification and installation according to GPL V3 needs the distributor's keys the GPL V3 gives a way to demand it of the distributor. There are at the least mixed signals coming from the distributor in this case it seems to me.
These proposed considerations only apply to GPL V2 "or later" licenses, stuff like Linux which is GPL2-only seem to have no risk that GPL V3 provisions might be claimed as duties for the distributor.
[1] http://gplv3.fsf.org/gpl-draft-2006-07-27.html
''1. Source Code ... The Corresponding Source also includes any encryption or authorization keys necessary to install and/or execute modified versions from source code...''
