Well, Wiki listed the original run for the first two series being from the 70s. Only the third series is from the 80s. So I guess it depends on which series you're talking about.
True, "The Simpsons" is a lot more kid friendly than Family Guy and American Dad are, That would be an accurate comparison.
Fair enough, I suppose. Family Guy does seem to overshadow it more in both ratings and popularity, though AD still gets pretty decent ratings even if it's not talked about much.
Yeah, I can't say I've seen the earlier episodes of Shin-chan, but all the later ones I've seen subbed seem really childish/tame. The ones I saw feel like they'd be fit for Nick Jr, even. One involved Shin learning how to go down to the post office and mail a letter, like an episode of Max & Ruby or Rugrats.
Hannah Montana does extremely well for boys and girls between the ages of 12 -17, it can even be the #1 show for the teenage demographic when there's a new episode. That's a lot better than Avatar and Naruto do for teenages, but you always see more Naruto and Avatar talk on the net. So I don't think age has anything to do with it.
I'm with the belief that the more a show is popular in IRL, the less it gets talked about on the Net because fans can find people in real life to talk about it with, but for more obscure/geek-oriented shows, like Avatar, Naruto, and other comic-book shows, the Net is probably the only place you'd find people talking about them unless you go to a Con or join a club.