Not to be contrary, but is this really so among more experienced dancers? For example, On what beat in the music does Tete step side at :40? By my count, it is on the and of 5. Throughout this piece he leads/steps off the compas, and lands off the compas. I have the impression that this was much more common among the milongueros of yore, who perhaps danced as much to the melody as the rhythm, than modern dancers who come to Tango with more of a rhythmic (think rock-n-roll etc.) musical basis than the golden age dancers. Thus the man/woman can't always rely on the music to compensate for imprecision in his/her lead.