I think, it's about perceived proximity (car, train, and plane, help to lower that) and the kind of relationship you want.
I have two girlfriends who live two train hours away from me. As the two implies, I'm not living a regular relationship, so I'm inclined to go to greater lengths when finding someone that fits.
Because when you spend enough time around anyone, you realize they suck (because everyone does). So some degree of grace is required as well to maintain love once the proximity factor has peaked.