i believe that is was 'designed' like that to test your real bench-press/chest-shoulder strength without the additional assistance you normally receive by placing your feet on th efloor.
And it just might be a great training method to use in an effort to increase your bench press max in all world wide bench press contests held today.
Do any of you Powerlifters ever consider traing with no foot on floor assistance nowadays?
I also tend to think that this high bench method coud have been initiated around the time that 'isometrix contraction' was in vogue, but I'll have to Google that to insure that I ain't as stupid as I think I am.