I've noticed that sometimes studios give the directors and writers more creative control if their names are big enough. If they're smaller names just starting up, they put the hammer down on them. That's why Rango and Speed Racer got away with some very PG-13 cussing (Speed Racer even had a flipped bird, something you can't even show on Family Guy) in a PG movie. Big names behind them. Any meddling was from the Muppet people, and their "meddling" actually punched up quite a few of the concepts from the original script, even making them better (Kermit's housing situation). Any studio meddling was probably just editing the movie down.