Basically betting is exactly the opposite of this scheme you're proposing. The fact that BitBet is doing thousands in bet BTC a month whereas an implementation of your idea doesn't even exist in practice should be sufficient empirical evidence that you're wrong. Why isn't it?
A lot of betting and trading sites have perished. Bitcoinica, Kronos.io, Mooncoin, Betcoin, Bitscalper...
Is there a reason why BitBet is more secure than any of them? Aside from operator being a buddy of MP.
BitVPS operator was also a buddy of MP, but it turned out he is an asshole, didn't he?
So "being a MP's buddy" is not a good criterion.
There is a more secure design than what aan have described, basically a third party controls whether Alice or Bob will be paid. (It cannot send money to Eve, though.) But if third party dies, Alice and Bob can settle it among themselves.
It is based on hash-locked payout script, I've designed it back in summer of 2011.
Implementation doesn't exist because people are way more interested to make a quick buck than to actually implement something worthy.
Also users are not willing to sacrifice a bit of convenience in the name of security.