This was probably the catch, because the second way does look better at first, but in reality they should be the same.
10 wins of 2 plus 10 losses of 2: 2*10+2*(-10)=0
8 wins of 2.5 plus 10 losses of 2: 2.5*8+2*(-10)=0
10 wins of 2 plus 10 losses of 2: 2*10+2*(-10)=0
8 wins of 2.5 plus 10 losses of 2: 2.5*8+2*(-10)=0