It's not really designating a key to open the chat box, it's for automatically opening it when you start to type. The letter keys on your keyboard don't have any function in the game other than to type (with the exception of y/n for destroying stuff when that interface is open), so it makes sense to open the chatbox when any letter is pressed. I'm no java programmer, but it doesn't seem like it'll take long to code at all. If the chatbox is closed and any letter is pressed, save the letter as a string variable, copy/paste the code to open the chatbox (from where someone manually clicks to open it), then throw the saved letter into the message line. I can actually see this being pretty useful for people who don't have huge screens or play on resizeable in a smaller area.