The bottom line is that test weight is not the same as kernel weight; and has nothing to do with yield.

10,000 lbs of grain delivered to the elevator at 15% moisture is 178.6 bu per ac regardless of test weight because we sell grain in 56-lb units; not according to test weight. 

   10,000 lbs of 50 lb test weight grain = 178.6 bu/ac (10,000 divided by 56)

   10,000 lbs of 60 lb test weight grain = 178.6 bu/ac

I agree that the concept of test weight is squirrelly. Some have argued over the years that it not be used as a measure of grain quality; notably Dr Lowell Hill of the Univ IL.  Folks routinely misconstrue test weight as equal to kernel weight.

I agree that it can be frustrating to deliver a level-full 1000-bu semi load of grain with a 50-lb test weight and only get paid for 893 56-lb units of grain [(1000 x 50) divided by 56]. On the other hand, it feels better when you get paid for 1071 56-lb units of grain when you deliver a level-full 1000-bu semi load of grain with a 60-lb test weight [(1000 x 60) divided by 56]. But, ultimately test weight by itself does not correlate well with how many 56-lb units of grain you harvest from a field.

I offer my recent article again for your viewing pleasure:

http://www.kingcorn.org/news/timeless/TestWeight.html