US CODE: Title 15, Chapter 1, Section 2.

[antitrust at usdoj.gov removed from cc's]

Karl,

>So I count one place: ARIN.

Actually, technically speaking, there are two.  ARIN and the IANA.

>There could have been others, but they have all agreed among
>themselves to carve the world up into exclusive zones in which each
>will have the sole and exclusive right to allocate address blocks.

"Agreed among themselves"?  Please see RFC 1466 and who its authors are.

>Perhaps we just ought to drop the geographic limitations and let the
>three registries allocate anywhere in the world.

This has been discussed in the past in numerous venues, however the major
sticking point is coming up with a way that insures the competitive
registries do not ease allocation requirements in order to obtain additional
customers without creating a huge bureaucracy of auditors.  If you come up
with a way, I'm sure all the registries (myself in particular) will be very
interested in hearing about it.

Regards,
-drc