Fed plays a very efficient game. It's good for him but for us audience it becomes monotonous, wall to wall action that can be boring. Fed's matches are usually entertaining because of the other guys, eg Murray's frustration, Djokovic's screaming, going for broke, etc. Nadal's game is great for TV cuz he's a master of displaying grittiness and determination.
Anyway, it'd be very very hard for Babolat to sell the APD if Nadal wasn't in the picture. Racket like the APD is a dime a dozen and so is Fed's. Every single brand has an equivalence.