Marathoners are almost as irritating and preachy as vegans (forgive me, I work out at Rip's gym).
I like mountain biking, but I will never be a great rider because I don't want to give up 30 pounds of bulk (and lots of training time) just to make a podium. It's a hobby, but not a focus.
Of course there are always exceptions. Some bodies hold mass while others go the POW route. Dean Karnazes, the ultra-marathoner, has a body that any CFer would be proud of.