The problem with the above actions is that the game company gets a piece of Customer 1's money, and zero out of Customer 2 because Customer 2 bought it from an unauthourized re-seller, who previously had bought it from Customer 1 with their own money for half the price. Just pretend Customer 1 was the game company and they sold it to an authorized seller. Game company will get a share of what authorized seller makes from customers. But when a second hand shop sells a game it got from a customer to a new customer, the game company gets nothing when they could've gotten something had new customer purchased from authorized seller.
I would like to link to the article, but I've no idea where I saw it. The EA rep then mentioned that one way to avoid the sales of used games is to make better games. With the possibilities of downloadable content, it is then possible to update said good game to keep players from parting with the game. EA's example of this is Burnout Paradise, which from what I've read is enjoying a nice life in the hands of gamers.
My take on eBay, that's another story. But since eBay's not alone in that field, I guess it's hard to stop selling used games in its entirety.