Tennis is a "game of angles," and greater height allows more angles. This, coming from a guy who's 5'8"
If Ferrer were Federer's height, he'd probably be #1 or 2. If Isner were Federer's height he wouldn't be Top 500.
"The Pusher" - my new ball machine idea. http://tt.tennis-warehouse.com/showpost.php?p=6764523&postcount=1