A rabbi discussing his Passover celebration (Emet Ministries) pointed out that even though the tongue is a muscle that's used all day long, it doesn't get tired. I just saw a reference to that thought on a blog too. I wonder what the implications of that really are? The heart muscle also works constantly, it keeps us alive. Oh, never mind, autonomic systems are totally a separate concept, it's the fact that the tongue is under our control that matters here.
Our tongue does work other than speaking so I guess it still makes biological sense without any need to read something else into it.