Some people simply like running for the pleasure it gives them. I guess it's the same with weight lifters. At some point the physique is a side-effect of one's regulard and healthy practice.
Note that sprinters as well as endurance runners have to lift some weight at one moment or another. When I run my first half-marathon I was surprised that my arms were more sore than my legs.
Why do people prefer to run for hours instead of a more intensive workout in a minutes?
Looking at the typical runners [0], why would you desire a physique like that?
[0] http://diaryofakalechic.files.wordpress.com/2011/08/marathon...