Actually, an exchange bets as much against you as any book...they simply claim they don't. 99%+ of all liquidity on an exchange comes from market makers which are, for the most part, owned by the exchange itself or at least have some kind of a shared profit deal. This is exactly the reason all exchanges now have some kind of premium charge in place to avoid bleeding too much from profitable traders. The statement that exchange don't care if you are winning because they only profit from commission is simply not true. They want losers just like any regular bookie.