Fox announced it's renewed "The Simpsons" for another two years. That means the show will soon become the longest-running prime time servies ever. Western "Gunsmoke" holds the record now, having run for the 20 years ending in 1975. What's the secret to "The Simpsons"' success? Its animation -- so it's cheap to make, its stars don't age, and it appeals to a wide demographic. Also, "The Simpsons" is very funny.