I wonder why, so rocks don't hit the cable? you would think they would just do it like that on their production bikes. especially since most riders shuttle at one point or another.... weird
most bikes run cables on bottom of top tube or ontop of down tube, not sure where anyones getting cables run on bottom of downtube because ive never seen a well set up dh bike with cables ran there. The only cable that is run on the bottom of downtube would be front der. (you can see the welded on mount pieces in this picture) which obviously isnt needed in dh.