The Cowboys decided they needed a fourth tight end more than a third quarterback.
They’re looking for short-term cover at tight end, because of the uncertainty over Witten’s health.
But mostly, the reality is that if you’ve got a quarterback you trust, you only really need two.
If anything happened to Tony Romo, Kyle Orton should be able to fill in capably for a period. But if it got down to the point where they were playing a third such as McGee, they’re in a world of hurt anyway.
That’s true of most teams with what would be considered good starters, as the third is a luxury that could be better used elsewhere.