You are talking in circles.
What's the point of having a three conductor plug, if the third wire is a putz and the female end only has two contacts?
Is there a third copper contact on the female end?
Do you really think there isn't?? That the metal grounding pin in the adapter is there just for kicks?
http://www.flickr.com/photos/74847775@N00/3928178121/

In the small channel either side is metal which makes a connection with the earthing pin on the MagSafe power brick. This earths the MagSafe and MacBook Pro.