It really does shaft the doubles specialists. Mixed is only played (I think) at the slams- and probably makes up a good chuck of money for some of the players (and it's not a massive amount of money for the winning pairs compared to the singles).
So itmust really stung to see the singles lot- most of whom don't need the money and are seeded in the top 20 - getting all the glory (and I bet the prize pot increases too).