If you look at Kenny's drawing, the cable will be against the front of the bed. By being against it, it will be lift the bed and opening the scissor lift at the same time, IMHO.
It probably would, but as things wear, the pull on it will be straight-line with the upper arm, then possibly over center as it gets older. By dropping the roller on the front, it alleviates that extra strain and makes the future assumed wear a non issue as far as pull is concerned.
I don't want to sound as if Im poking holes, I think it's a great design and will do one heck of a good job. Just trying to prevent a problem in it's later years.