I don't think these messages help at all. For one thing, they can just delete them. Another thing is that I doubt most people look at someone's profile within that 30 second time for the auto abort before the game starts.
Pen2da_Pixel also has a point.
When a player disconnects when they are losing, I wait till the server times them out -- then I leave a note on their homepage about their poor sportsmanship to warn others. It ain't much, but maybe it will help to discourage this habit.