What you bought is a license. It's the same thing as buying a ticket to an amusement park, all you get is a conditional and revocable privilege to enter the park. In the case of Guild Wars, it is a not a transferable license, which is stated no less than 4 times in the user agreement, so the only person that is allowed to use your account is you (or strictly speaking, a minor you're the parent/guardian of).
http://www.guildwars.com/support/leg...-agreement.php
Also, read section 4(c) if you want to know how much you own, and remember that you agreed to that provision multiple times.
As for the Autodesk case, keep in mind that Guild Wars is not simply about owning a copy of a piece of software, it's about having a license to access the service as well. Enforcing the non-transferable nature of event tickets, for example, has stood the test of time quite well.