1. the guy is only an example. Willpower alone will not make you run 100 mile-race. You need the right body as well.
2. most people don't try and run 100 mile-races because they have better things to do
3. willpower and success: seriously this is really self congratulatory. running 100 miles does not make anyone a more succesful person.
4. no mention of endorphines and running addiction?
You need to get in shape first, obviously, but unless you have a condition that prevents you from doing that, you can do it.
I get the impression you haven't done much distance running, because the article is spot on when he says it's almost exclusively about determination.
#2 just seems like you're being a dick. #3 is unprovable, and #4 is something I rarely hear any serious runner talk about, and it certainly isn't the reason I run at all.