Zombies Rise from the Sea
I think that explanation is too convenient. Kids aren't any more susceptible to liking things that are on the screen than anyone else. Put a boring show on the screen and watch what happens. And they won't laugh at jokes they don't understand. Can you imagine kids (if they watched it) laughing at "Ugly Americans"? (I'm not saying it's especially funny. I'm saying that just because something appears on screen doesn't mean kids will be entertained.)
I have to slightly disagree. I mean the "things that appear on the screen" usually refer to energetic, wacky and lively. The Simpsons has a ton of animation that seems to focus on the action rather then on the environment. I mean you have Homer spinning around, narrowly avoiding stuff and being lifted up and down... There isn't a complex joke in there that'd go over viewers heads, it's all animation. There's also the funny voices, the gags which involve Homer being one thing then another thing (The mirror gag, the car gag, the invisible cash ATM gag.) and the occasional action sequence. I mean why do you think Spongebob Squarepants and Aqua Teen Hunger Force have gone on for as long as they did. (I do agree about the explanation being convenient, I mean there are tons of Kids shows on PBS that rely mostly on the characters and situations and not just the animation/funny voices/action. However, it does apply in a sense that The Simpsons have these wacky mostly animated moments and these jokes involving funny voices, such as the one I mentioned above.)
On an unrelated note, I would guess that younger viewers would not like the older episodes as much as the newer episodes if they've seen them first; but then again, they'd begin to see the older episodes as good as the newer episodes I'd guess...