Steam does not give them nearly the same sales as elseware. It is nice but most still get it elseware otherwise they would have gone with Steam completely to remove the resale issue and some actually have. Valve obviously for instance does not have to worry about resell on PC and enjoys a somewhat effective anti-pirate solution. And they do lower prices on steam alot. It just that Valve prefers them to save up and do a big sale with other products at the same time. The Xmas sale, the summer sale. Prices do fall when resell comes out of the picture. So they can award those with a keen eye and a knack for patience.
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I guess we'll have to agree to disagree, because I don't see any way that restricting resale is going to lower prices - normally when a seller has you over a barrel, he doesn't give you a break. But for my wallet's sake, I hope you are right.