This:
is retarded.
The average chance of victory is indeed 1/2 (assuming no people have the same amount of money). However, if A is taken as the amount of money, the case at hand is no longer the average case. The chance of victory is now contingent on A.
Now, consider there be n people with money A_1, ..., A_n; A_i < A_{i+1}. The player can be any of them with no way of knowing which one he is, as per the initial presumption.
For the person #i, the expected winnings against a random opponent are (- A_i * (i-1) + A_{i+1} + ... + A_n)/(n-1), because in (i-1) cases he loses all his money, and in (n-i) cases he gets the money of that opponent.
Totalling that up from i=1 to n, we get 0: for every A_i that is subtracted with the coefficient of (i - 1), it is added i-1 times in the previous members. Thus, the expected winnings with the position in the list being selected at random are 0.