A book that steals from its smartest 1% of its customers can go from deep red to deep black. Wageweb is using the same MO used by Sportsbook.com -- treat most people fairly, and screw hard the ones that are smart enough to beat you.
If you got lucky and beat Wagerweb out of 20k, I think they would likely pay you. If you beat them with your brain, they didn't have a chance, and they figure this out, you're not as likely to get paid.