Was this the case here? How is that they didn't spot multi accounts before player won, but as soon as they start withdrawing...."peanuts", SB investigated account? Oh, wait, never mind 
I think I have a bulletproof 100% winning strategy. I'll share it for free just because I'm generous today. Regular price 300 BTC.
Create an account on Sportsbet. Make ludicrous bets. If you win - great. If you lose - create another account, contact support and say "hey, I have multiple accounts". Technically they should allow you to withdraw the deposited funds and cancel the losses like they cancelled the winnings here. To make it extra bulletproof, create both accounts in advance.
This whole multi-accounting thing is idiotic, no question about it. But I don't think there was a violation of a written contract here. Written contract, stupid as it is, gives Sportsbet the right to do what they did.
- smiley because some dildo will surely think I'm being serious with my "strategy".