I did suspect there was some tongue-in-cheek in your post
But in the example you give there, it looks to me as though at 3:15 he simply counts them in. How do they know what his varied flailings mean? Well, that performance isn't the first time they have worked with him - there will have been many months of rehearsals involving discussion about the performance as well as playing (and more than likely a lot of shouting from the conductor when members of the orchestra fail to understand his flailings).
He is not just keeping them in time but controlling their expression too. If you ever watch an orchestra without a conductor you will see they are shit. Individual sections may stay together, but the piece will quickly lose its coherence.
( tangledupinblue hairy badge with moving eyes, Fri 23 Sep 2011, 12:40, Reply)