Invghost: Broad answer to both replies: The system can be abused with refunds anyway.
Refunding doesn't give you a game you want, it just allows you to give back a game you don't want. It doesn't limit the pool of games you could get.
Different thing.
Also: Finding one Steam account once that suit your needs is different from buying and refunding again and again and again.
Invghost: In response to the fact certain people want certain games from the pool, then once again, they'd have to find a person with a ton of games that didn't already have that one game they wanted, just to increase the slim chances of getting it.
I don't think that would be really difficult. :-D
Also, giving people an extra incentive to buy games on Steam when they're cheap there so they might even have an advantage in the next GOG random sale thing might not be in GOG's best interest IMO.
It would mean that GOG rewards people who own many Steam games and especially those with games they could also buy on GOG.
Edit: Sorry if I stop answering, I have to be off in a few moments.