And so, if you want to sell the game, it's all about transferring the serial number - however, that automatically also means to share the account, which is bound to that serial, if it was used to download content already. Or so I think. I'd be interested on what stardock thinks of that matter? Whether they find it ok that people resell their game or not.
Obviously a resold game is lost revenue for them. However, if every one of the 100.000 who bought galciv2 already did sell his game and the game was then resold, say, twice again, that makes a potential of 400.000 people who'd be inclined to buy galciv3. So a reselling policy might have it's disadvantages, but also advantages. Probably depends on whether it's a short-lived company or a long-term planning one. So far it looks like the latter case.

(Which I quite like)