Having read his journals and posts about his tours, I have no doubt that Cyclesafe is reporting his mileage accurately. 20k is not an unusual amount of miles on a bike for someone who rides much.

I have not ridden much at all in the last 5 years other than when on tour (I trail run and don't ride at all most of the year). Yet even I have a little over 10K miles on my touring bike. Given that I didn't ride it at all in 2008, rode it for only about 10 days in 2009, rode it for only a month in 2010, and it hung from a hook in the basement pretty much the rest of the time, it would seem to me that 10K miles is really very light usage. I did ride it a lot in 2007 when I did the TA and rode it near home some as well. So basically I rode it something like only 150 days in 5 years and still racked up a bit over 10K miles on it. I don't have any reason to think that there aren't a ton of folks on this board who have ridden at double, triple, quadruple, or even more times what I rode in that period.

Someone who commutes 250 days a year 10 miles each way racks up 5K a year without even going on any long rides on the weekend or doing any tours.

When I was racing and commuting by bike, 10K per year was a normal year, but some people ride substantially more than that.