Since the original Muppet Movie was released in 1979, Muppet movies have received five Oscar nominations, all in music categories. This is the first time they have won. With only two nominees, if they hadn't won it would have been disappointing to the point of embarrassment.
There was an article in Entertainment Weekly this week about how the Oscars were more populist in the 1970s. I don't want to disagree because I don't know that much about it, but it seems to me that if they were really that populist, the original Muppet Movie would have gotten nominated for something other than music. Like Best Original Screenplay. Even the most cynical among us would have to admit that it certainly was original.
And if there is a legitimate case to be made for Andy Serkis getting nominated for any of his mind-bogglingly brilliant motion capture performances, there is (at least) an equally legitimate case for the Muppet performers being nominated for acting awards. It's kind of an interesting paradox because they work so hard to develop the characters and create in them the illusion of sentience and self-sufficiency, with the result that the puppets end up getting all the credit for their hard work.