So asking refunds for things you don't like or you bought two months ago is not exploiting?
There was no refund system two months ago so as long as people played less than two hours I don't see it as unethical in this beginning phase.
If a game doesn't work because it's bad, you are entitled to ask a refund. If you don't like a game, or you bought it yesterday and today the game has been bundled, you are not entitled to ask a refund.
Yes you are as long as Valve allows it. The refund system is not solely for broken games. Is this such an exotic concept for some people?
When I order something online I can return it for two weeks without stating any reasons and it also just works and it's a good thing for the consumers.