Rick's strongest skill must be his ability to keep saying "no" again and again and again and again where almost undoubtedly any of us would have said "yes" - that's what's won him the ultra-high sales over the years.
Basically, he's used 7,000 hooks (his domains) to bait just 16 fish. Even if you do the math on his renewal bills, he's come off pretty well - but it's an extraordinarily gutsy move to keep having to come up with US$60,000 a year in renewal fees, every year - then at the same time looking 99% of offerers in the eye and saying "no".
Put another way, he's sunk (in renewal fees alone, without even looking at acquisitions) over US$1,000,000 keeping his portfolio registered over the last 12-14 years. And in all that time he's sold less than 2 dozen names.