Precisely. With the introduction of shows like Family Guy and South Park, The Simpsons has become plain and dull. South Park pushes the limits (especially the later seasons), like eMad said, and that along with some funny, crude jokes makes it interesting to watch and also very funny. Family Guy is random, and also pushes the limits (though not as much as South Park), and that provides some of the funniest lines around.
The Simpsons on the other hand is becoming tired. They can't seem to produce anything remotely funny anymore, even for The Simpsons, and the older episodes have been viewed at least 5 times per teenager (and some adults). They've done everything they can with the humour they provide, and if they want to keep going, maybe they could start pushing the limit, even just a little, but still keeping The Simpsons style.
It's too "kiddy" now-a-days. Family Guy and South Park are the new wave.