I read the thread (mostly) and can perfectly understand why OP asked the question elsewhere. Maybe he wanted an actual answer instead of ranting and raving and purposeful derailing of the discussion that went on in that thread.What are you talking about? The OP made the same thread on the 2k forums and was given the answer. That is why I am asking whats the point of asking the same question here.
From what I could gather from the thread in 2k forums is that at least it is generally believed that Steam does not support onsell of the games. Steam EULA is a bit ambiguous on the subject though. Only part that says anything related I could find was: "You are entitled to use the Software for your own use, but you are not entitled to: (i) sell, grant a security interest in or transfer reproductions of the Software to other parties in any way, nor to rent, lease or license the Software to others without the prior written consent of Valve..."Ooh, that's a good find (although it shows you how I, like most people in the world, don't actually read EULAs ). My fear is that Steam itself has its own EULA that is far harsher.
On the other hand Steam EULA defines Software in following manner: "Steam and your Subscription(s) require the automatic download and installation of software and other content and updates onto your computer ("Software")." So in essence they define Software as the actual binaries and then say you can't sell them forward. IMO, there really isn't any clause in either 2k or Steam EULA that would explicitely prohibit selling pre-owned product.
However, since Steam provides the registration service, if Steam support says, they won't let you deactivate the product despite EULAs not really covering the issue, there isn't really much anyone can do apart from takin legal action. Though these kind of restrictions irritate me to no end, it's really not worth fighting a costly and tiring legal battle against large corporation for 50 bucks.