The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the Program specifies that a certain numbered version of the GNU General Public License “or any later version” applies to it, you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of the GNU General Public License, you may choose any version ever published by the Free Software Foundation.
Note the "or any later version" verbiage in there. If the software is licensed under "GPLv3 or any later version" - no permission is required or assignment of copyright.
In order to make sure that all of our copyrights can meet the recordkeeping and other requirements of registration, and in order to be able to enforce the GPL most effectively, FSF requires that each author of code incorporated in FSF projects provide a copyright assignment, and, where appropriate, a disclaimer of any work-for-hire ownership claims by the programmer's employer.
> The "why they require a CLA" is for enforcement.
None of that seems like a "why" to me; to cynically paraphrase it, "our policies require our polices." Why does your record-keeping require a CLA? Why is a CLA required to enforce the GPL?
A CLA is required to be able to sue someone infringing the GPL and represent yourself as the legal owner of the entirety of that code. If you have a hugely fractured ownership like Linux, it may be very expensive to bring a suit against an infringer.
