You could be right but Adobe obviously choose not to enforce that by wiping the prior version automatically.
I have to confess that I do not have the enthusiasm to troll through the agreement right now to clarify the legal postion.
Nonetheless I doubt Adobe have any intention of leaning on individual users on this.
Also, in an evolutionary sense, although I still have Lr 3.x on my workstation mainly for technical comparison of some issues, Adobe has succeeded in making Lr3.x functionally obsolete with the magnificent changes found in PV2012 (obviously prior Process Versions are still accessible) and the Print module, the Book and Map modules notwithstanding, I don't want to use prior versions for any serious work.
Regards
Tony Jay