Imagine if they sent you each game on a separate CD and told you "but don't sell the ones you don't want", you'd think that was ridiculous, right?

That's exactly how stupid this idea is. I own the products I purchased, just because it's not a physical copy doesn't mean I have any less rights to it. I highly doubt their ToS would hold up, I consider it highly immoral to attempt to deny people the rights to sell or trade their own purchases.