Vanity factor? How about being able to mount devices to the top tube without having to worry about crimping the brake cable, or putting it on a car rack and not having to worry about the shift cables on the downtube? My bike got pretty messy last November and being able to wipe down the entire bike with no external cables getting in the way was a big plus.

And aside from that, yeah, it does look better.

Cables are easy to replace unless they break off in the middle, just attatch it to the old one and pull it through. Trek uses guide tubes which pushes them in the right direction and stops them from rattling.