Basically, it means that you don't own a game; you own a license to play it. And that resale of a copy is prohibited unless expressly authorized.
Thing is, that's pretty much standard legal BS that every company would put down. They reserve the right to do those things, but it doesn't mean they're actually gonna do it. They just put it down in the Terms to cover their ass.
They're not gonna actually enforce anything.
Terms of use that we're debating today simply say that you may not sell the game without permission. "You may not resell any disk-based software or software downloads, unless expressly authorized by us..."
That's not unreasonable.