Her reply: I figured out what makes Mod Fam funny. Misunderstandings.
Boom! After thinking about it a while, I know this is right.
When you think about, some of the best sit-coms are the ones where communication and interpretation is often clouded. Those scenes when characters and subplots interconnect. You can see this in more popular shows like Seinfeld, Friends, and Fraiser that dominated the 1990's.
This show takes a sentimental look at the modern day family, and what family exists without its share of misunderstanding, really? I think this is why it works, because we watch some of these scenes and think, "I can relate to this!"
One of the characters that does this well is Phil Dunphy, played by Ty Burrell. He really means well, but his playful spirit often ends up being hurtful (which is what makes it funny, because intentional hurtfulness is not).