Also, just because we know what that the query port is the port that Steam needs to communicate with the server doesn't mean that the client knows it. Think a few years back, before you started messing with game servers... You didn't know what a query port was, right? I didn't, not until I had to know what it was used for.
For us it's just common knowledge, but sometimes it's a mess trying to explain to the customer why he can't use the 'real' IP in TCAdmin. You're not even able to join with the game port, nor search for the game, so it's just pointless that you can't set the game port equal to the query port.