You're absolutely right but this is what we're saying...
Let's say you hadn't posted in this thread. And, let's say I wanted to tell Gimpdiggity he should PM you for more information about (something). Without you posting in this thread, your name wouldn't be here to click the drop down options for. But, if this vBCode we're talking about was implemented I could type something like this:
Gimpdiggity, PM [pm]alaska cajun[/pm] for more information on that thing...
The code serves as shortcuts for links you might otherwise have to dig for. Without you posting in this thread he'd have to search on your name to find one of your posts, THEN click on your name for the very menu you're speaking of - or he'd have to go to his UserCP, go to Private Messages, then "compose".