Yes, I agree. Averages really do not apply to Halves. Simply the luck of the draw.
I will say this If you want to talk averages.
I average more silver when I search Halves.
My feeling is that the 1/2 dollar coin does not circulate so the majority of the ones that do eventually get turned in at a bank will contain Silver because it is an accumulation that has been hoarded for many years.
I think you could ask just about anyone and they would tell you that if they kept any coins at all since childhood it most likely would be a Half dollar coin.
My Opinion.
Mojo