You don't buy the game, you buy a license to use (play) the game. You don't own the game. The license is non-transferable.
That being said, of course it is unfair, but unfortunately that is how the software industry tends to work. I have good hope that this will change in the future, since games, and in fact any shrink-wrapped software is a commodity, and it should be possible to trade it like any other commodity.
Then again, you can sell your non-transferable non-refundable airline ticket to someone, doesn't mean they will be able to fly.
At least stardock doesn't use copy protection on the game. You can also download the 1.0X update without the serial number, so if you bought a used 1.0 retail version you can update it to that version. I doubt they will release 1.1 to the public, unless they start selling 1.1 retail. Finally, you can buy a new serial at a discount.
Other game publishers make all updates publicly available, but they use nasty copy protection software to protect the CDs or DVD. However, at least you can buy second-hand games and update them to the latest version. Stardock doesn't use copy protection, but instead you can't update your game beyond what they sold in retail boxes. Personally, I think that is the lesser of the two evils. The amount of time I wasted, er, spent playing the game so far is way way more than I spent working to earn the money to buy the game. In addition, it gives a good feeling to support a company which is less evil than most other software companies out there.