To add to Pastor Wallace's point, the picture in the NT is of teaching and oversight going together. When one person does all the preaching from miles away, not only can't he oversee, he can't adapt the teaching to the particular needs of the congregation.
Excellent point. I was thinking about that very thing demonstrated in a dramatic way a few Lord's Days ago. The preacher was prepared to address a certain text in a certain way. He had his sermon notes before him all laid out when one of the members of this local body collapsed and had to go to be taken to the hospital (happily, he was stabilized and is now doing well).
After the excitement was over and order restored, the preacher began his sermon on the same text, but he put his notes aside and focused on the Sovereignty of God, the frailty of life, the call of the Gospel, and the unity of the local church.
It was exactly on point and what was needed by his congregation. A satellite-fed preacher has no way to look upon the faces and expressions of his flock and adjust his message to immediate concerns and circumstances.