I always wondered what was meant when Stewie from Family Guy said "Jim Henson took a wait and see approach and now we have wrong sounding Muppets".

Then I watched a biography of one of the more prominent Muppeters, Kevin Clash (Elmo). Very enlightening biography, it's called "Being Elmo".

Back on topic, apparently in 1988/1989, I forget now... Jim Henson was with Kevin Clash on a talk show appearance with Kevin operating a second Muppet. After the show Jim complained of a sore throat.

2 weeks later he died.

Nowadays, while Frank Oz is still alive, none of the Muppets voiced by Jim and Frank have their original Muppeteers. While I don't know who voiced Gonzo, he has a new Muppeteer and definitely sounds different, more like his Muppet Babies self than his Muppet Show self.