Orwell's original essay says: > one should drink out of a good breakfast cup—that is, the cylindrical type of cup, not the flat, shallow type. The breakfast cu

Orwell's original essay says: > one should drink out of a good breakfast cup—that is, the cylindrical type of cup, not the flat, shallow type. The breakfast cup holds more, and with the other kind one’s tea is always half cold—before one has well started on it. So I suspect that "tall" is a byword for "not shallow".