You do have a point, but then you run into the possibility of getting a bunch of unsolicited trade offers piling up that you have to deal with, as well as the question of how long trades should stay open before the expire, or how many times you can jump back and forth with changes, and so on. I don't have a whole lot of experience, but all the games I can think of with individual trading systems all operate in real-time.
All right, one final bugging. The only one I still need is Skyrim, and I have extras of Dead Island, Football Manager, and Torchlight. After I get Skyrim, I'll still trade 1:1 if people need one of the extras. My profile name is PD_Top_Gun, since I don't think I've mentioned that.