I already accounted for the difference in Federer's serve. It has more to do with his preparation and trophy position than the racket drop itself. Take a close look at the orientation of the racket face at the trophy position for Federer (and Sampras). Much, if not most, of the racket head drop is due to ESR. When Roger externally rotates his shoulder for the drop, the face will naturally face upward given the orientation of the racket face during the trophy phase.
Now take a look at the orientation of the racket face at the trophy for Pancho or Rod. When they externally rotate the shoulder for the racket drop, the face is one edge rather then open.
Stanimal's prep and trophy appears to be somewhat different. His elbow position at his trophy is a bit high (not in line with his shoulder tilt like most elite servers). Not certain, but it also appears that he might employ more elbow flexion and forearm supination than other elite servers -- most use ESR w/o extra flexion.