Has The Simpsons changed significantly in essence with time?

In the old days one could easily empathize with some characters, thus many situations ended up as funny ones.

Now a days, it's like they try to convince us to empathize with them by giving some explanation, or justification, or a character's actions. It seems like all characters tend to justify their actions somehow, as a parody of themselves.

Could those changes be due to a change in the target audience? How has the show objectively changed over time?

Initially, the show was intended as a broad audience. I started watching the series as a kid, and even as an adult I find it funny, at least the earlier seasons. Now the show seems more like SpongeBob SquarePants or The Fairly OddParents.

Update

The following are some interesting data:

Source: http://en.wikipedia.org/wiki/List_of_The_Simpsons_episodes#Ratings

Source: http://anepigone.blogspot.com/2012/04/ranking-simpsons-seasons.html

List of showrunners throughout the series' run:

• Season 1–2: Matt Groening, James L. Brooks, & Sam Simon


• Season 3–4: Al Jean & Mike Reiss


• Season 5–6: David Mirkin


• Season 7–8: Bill Oakley & Josh Weinstein


• Season 9–12: Mike Scully


• Season 13–present: Al Jean

Source: http://en.wikipedia.org/wiki/The_Simpsons

Maybe it could be related somehow.