Quick! Who played the title role in WALL-E? If you answered "Ben Burtt," chances are you're either a hard-core geek or someone who stayed for the credits and thought, "Who the heck is Ben Burtt?" Burtt, well known to Star Wars and Spielberg fans for his superb work as a sound designer -- he's won two Oscars and received two Special Achievement Awards from the Academy -- picked up his first credit as an actor for providing WALL-E with a voice. And he drives home the point that cartoons, or "animated films" if you prefer, don't need celebrity voices anymore.
Once upon a time, Robin Williams agreed to voice the part of Genie in Disney's Aladdin. Disney decided to capitalize on his stardom and advertised his supporting role heavily, probably the first time a celebrity voice was used to sell an animated film. Aladdin became the biggest hit of the year. This was the tipping point. Millions of adults, notably those without children who hadn't been convinced by the previous year's Beauty and the Beast, decided that cartoons were not just for kids anymore.
The rest is history. Celebrity voices became the norm, and if one celebrity helped bring in the box office bucks, three or five or seven must be even better, and voice casts soon became filled with celebs both major and minor. Celebs had another advantage: they could give interviews and go on talk shows to promote the movie. Inevitably they'd say, "I wanted to do something my kids could see."