an inner guide makes sense if you store it out of the rain and dry it after wet rides. The brake cable housing can rust solidly to the guide tube, thoroughly bumming the owner out when it is time to change housings.

On a related, less painful note: you bend a tiny hook in the end of a broken spoke, run the cable into the frame, and fish the cable out with the little hook. Then run the cable housing down the cable wire and it'll pop out at the other end. It's easier than it sounds...Kleins have no internal tube and they work in a similar fashion: run an inner lining into the frame, fish it out with the little hook, and then run the cable wire.