Whatever Happened to TV Theme Songs?

So, I recently downloaded the theme song to "Sanford and Son" to my iPod. Before you judge me, this is a great song. And, as a TV theme it's perfect. When you hear the song, it sounds like the instruments are found in a junk yard. There's funk in it and the overall tone captures the shambling spirit of the show.
As I listened to it, I thought about how great all the shows in the 70's and 80's used their theme songs to capture a feeling or mood about the show. Typically, songs with lyrics were organic to the show. The lyrics usually summarized the show or set the tone. Today, if there are lyrics they very rarely fit the show's content.
This is a short post, but something I've been thinking about recently. I wish we had more singable or recognizable themes. Even the old themes without lyrics set a tone. Think about "Barney Miller" or "Night Court". And, pretty much any show created by Norman Lear (Good Times, The Jeffersons, Maude) or Junger/Witt (The Golden Girls) had a song that made you fondly recall the show. I am pretty sure that these themes made the shows better and kept them on the air longer.
So, check out the themes now. You'll see that they are actually really good songs. They stand on their own merits. I wish TV shows had that today.