One more thing tangentially related to the premiere of Sit Down, Shut Up: one of the things most commented-upon (apart from the live-action backgrounds) was the fact that the characters on this show actually break the fourth wall at times, saying that they “won’t test well,” or turning to the camera and saying “we’ll be right back.” This is unusual because while comedy cartoon characters have traditionally been very willing to break the fourth wall and admit they’re only fiction, characters in prime-time cartoon comedy are just the opposite. You can count on the fingers of one hand the moments when, outside of Halloween episodes, the Simpsons have talked to the audience or mentioned that they’re on a TV show. (When Homer said “we’ll be right back” before a commercial break in an episode from the 11th season, fans were so shocked that it became a subject of online debate.) Even South Park characters almost never talk to us or otherwise break the fourth wall. You’re more likely to find characters stepping out of the show on a live-action series, like Moonlighting or Boston Legal, than you are on a cartoon.
These cartoons have lots of reflexive, self-referential moments, but they almost always do it without letting the characters acknowledge that we’re watching them. (Futurama went too far with this, having dozens of arch little meta-jokes that the characters themselves didn’t seem to get.) It’s like the writers of prime-time cartoons are concerned about making sure we can believe in the characters and not think of them as “cartoons” — which means, among other things, believing that they can get hurt or die and that their actions have consequences. That means making the characters believe in what they’re doing, and not winking at us.
One exception to this rule was Duckman, where the characters broke that wall with abandon, but that show wasn’t actually a hit, and that might have been one of the reasons why.
I guess Family Guy has more fourth-wall moments now than the other shows do, but I don’t know if that’s an exception that proves the rule or just an example of how the Family Guy writers don’t even pretend to care. Anyway, even FG will usually try to find a substitute for fourth-wall-breaking, like when Brian told Stewie that “if I were someone watching at home,” he’d be very upset about the way a particular adventure ended.