No, I don't think so. Thieves don't normally go on a buying spree of "sale" items. They steal what they want whether it's being offered at a discount or full retail, because stealing is what thieves do. Free is the ultimate discount, after all.
I'm not saying that it would eliminate piracy. It' just that I think some people turn to piracy because they just can't afford the games, and if the games were considerably cheaper these people would buy them instead pirating them.
Does anyone know what percentage of a games price goes to the developer?