Can you share a little more about what makes 20,000 a magic number? How is it derived at?
It's "touted" as an appropriate tipping point of the difference between what you'd pay over-and-above the direct costs for a domain (vs what you buy from a reseller) which makes the paperwork, membership/fees/etc be worthwhile
It's based on an "assumption" which may or may not depending on yoru systems, staff, business etc be correct that all "costs" for providing a domain regsitration service are as low as thos from turnkey "systems" providers
What it boils down to is something like:
ICANN Fees (average) $4000 per year, signup costs (inc paperwork, solicitors, LofC etc) $6000
Per domain costs (10$ verisign, 50c ICANN, 1$ dns/whois/software)
= 11.50 each
Sell 20,000 @11.50 + 4000 + 6000 = 240,000$ = $12 each
If $12 is the price you can "buy" them from a reseller for, it's only after that 20,000 it makes any financial sense to *consider* direct accreditation
(obv. figures rounded up for simplification)
IMHO too many people jump into it without understanding the real costs and work involved, and the knock on effect of their busienss, which is why every year to number of overall regsitrars doenst change significantly - as many sign up as get acquired as get de-accredited for non-payment of fees.