Stairs in TV....... the regularity in the world of sitcom

Just before I was watching American Dad, and something struck me.
First it was the opener. I noticed, that during the opener, in the part when Stan (the all macho typical Dad hierarchical figure) is singing and comes down the stairs, he sings towards 2 photo frames. One is the statue of liberty and, the other is Jesus.
I thought about it a bit, thinking, "hmmm, a show like this paying tribute to religion? How odd...."
I thought about it once more and remembered how the two frames were portrayed in relation to each other. And the statue of liberty photo was much bigger than the Jesus one.
Now that makes more sense. A tongue-in-cheek cartoon slyly making remark of the typical American families greater love for its country rather than its religion.
This got me thinking to my good ol' uni days, of studying film and tv and trying to make sense of it all, discovering hidden meanings behind apparently unmeaningful and basic surroundings.
And just like that it hit me: why so many stairs in American sitcoms? Staring at me in the face, there it was, on American Dad, stairs leading down into the main living area. And without even trying I knew there were countless more out there.
I quickly did a google search, wondering if my sudden realisation had already been written about by some aspiring-professional uni student out there.
And lo-and behold, I found it: http://tvtropes.org/pmwiki/pmwiki.php/Main/StandardizedSitcomHousing
On a site called TV Tropes, dedicated to the tricks of writing fiction, for many forms of media. The article I read in particle was called "Standardized Sitcom Housing." Just like the title, it observes and describes the
typical sitcom house, and gives some good examples of where this has played out and in what shows.
Along with stairs, it talks about where the front door is usually situated, along with the positioning of other entry doors, the living area, kitchen, etc. Popular shows that include this layout are Full House (an old fave!), Who's the Boss and The Fresh Prince of Bel Air.
And which other show complies with this model? American Dad. A little pat on the back for me, I've still got it, my uni days aren't that far behind....
Looking into things a bit too much, can be fun :)