OPEN CHALLENGES aka weak points of the concept :
5) How to decide the event outcome without necessity to have human referee/judge ?
Without (super)human level AI I don't see how that is possible. For example, a boxing match is decided by the judges, who are human. If you want to bet on it then you are at least relying on the judges, unless you have a super-AI that can say, "The judges scored it 112-110 for Rodriguez but I am awarding it to Lopez instead". I think that would cause more disputes than relying on humans!
Some event outcomes could be defined in terms of observable events on the web. For example, instead of betting on whether Miami Heat will beat the Trail Blazers you can bet on whether Yahoo! sport will display a greater score for MH than TB at such and such an URL at such and such a time. This removes the site operator's discretion but introduces problems of its own.