Let me turn the question around a bit. Suppose N small providers peer
at M places and together represent p% of the Internet. If they simply
appear at one NAP and don't contract for transit, they may reach
100%-(%p/(M-1)) of the Internet. Is that something to encourage? If
they must contract for transit and as a result reach all major
interconnects, they get 100% (possibly minus a small epsilon for other
reasons). They then don't need to be at any of the NAPs. Are some
providers trying to show up at one NAP only with the aim of not
contracting for transit through anyone even though they can't really
reach others like themselves at a different interconnect?
Or, possible some small providers buy a multi-megabit circuit from a
large provider who gives them transit. The small provider then connects
at a single NAP and picks up bilateral peering sessions with a bunch
of people there. The result is offloading traffic from their
"transit link", which stands a good chance of being priced as a
"burstable" link. (pay for what you use) That gives the small
provider an economic incentive to operate in this manner.
No comment on whether this is a good idea or bad, but I understand
the thinking.
davec