Think its more a case of people being confused by the terminology.
Most people, I would guess, associate [b]DM[/b] with [i]Dungeon Master[/i], which in roleplays are interchangeable with [b]GM[/b] or [i]Game Master[/i].
Especially since the tab up there on the navigation-thingy does say [b]PM[/b] for [i]Private Messages[/i].
Took my brain a bit to acclimate to how NoCo says it too. :P