Well thats all fine and good then, but there's an awful lot that you non-americans don't understand because the shows are generally written for an american audience of a certain age.
Family Guy is set up the way it is to satirize the generation X american, who watched TV in their youth and just accepted how utterly absurd and dumbed down some american TV was in the late 70's, 80's and 90's. All those "like the time" sidebars are satirizing our short attention span, and throwing in little bits of culture that blast some of us out of our chair because we haven't thought about them in years (i.e. Stewie caught in the Sesame Street pinball machine, that one made my jaw drop.)
American Dad is written to satirize the middle class american, our overdeveloped sense of entitlement, and our sometimes ridiculous tastes. I like how most of what Stan and his family do are generally self serving, basically they're all a family of jerks. It wouldn't be much fun if they were NICE people. Roger is perhaps the best jerk of them all because he will go as far as take on a million different identities to find a new way to be a jerk.
The Cleveland Show I think was created to address the amount of racism in Family Guy, because as all the racism was showing just how stupid middle class white americans can be, however no one was making fun of black americans in that way. Since every group deserves just as much satire as the rest of us, The Cleveland Show was born. Maybe the writers were waiting for an event like Obama becoming president before introducing a show of this type, so the prudes can't whine about it? I think it's pretty damn funny.
One little note about the show that you may not be aware of, that is a joke in and of itself, the redneck guy on the Cleveland Show is voiced by none other than Kevin Michael Richardson, who himself is black! When I realized he was doing the voice thought it was hilarious.
These shows do so well I think because there is NOTHING like them anywhere on TV, and the basic point of them is that we ALL are stupid in some way or another. There's nothing quite as entertaining as seeing your own overdeveloped opinions being just as stupid as everyone else's.
