It actually takes away from him. The reality is that many, many people WOULD be capable, if they displayed the level of dedication that he does.
(for background: Scott Jurek is definitely one of the top ultrarunners of the current generation)
His athletic accomplishments are pretty awesome but you're right - Jurek and others make up the elite of the sport.
Not correct. He has won the Badwater 135 Mile and the Vermont 100 Mile ultras, and has come in fourth place in the Western States 100 Mile (iirc).
Jurek has a more impressive record than Karno as an ultra runner, and a history of being negative about not being as well known as Karno. Karno is a great runner who also wrote a great book and got a lot of people to read it and has a history of being positive and encouraging about everyone running.
Edited to add references:
First place at Badwater 135 Mile, 2004: http://www.badwater.com/results/index.html
First place at Vermont 100 Mile, 2006: http://vermont100.com/html/2006_results.html
Fourth place at Western States 100 Mile, 2003: http://www.wser.org/results/2003-results/