There are all manner of theories. Some have compared it to physical
land (possibly apt due to the limited nature of both), or to the way
land was granted to the railroads to spur development, etc. Spinning
the issue in any of several different ways could land you at wildly
differing results. I'll bet that significant bodies of relevant law
for each are contradictory and confusing at best. 
Anyways, my original intent was simply to point out that there are some
impediments to IPv6 adoption, somehow this morphed into a larger topic
than intended.
... JG