Media buyer John Rash goes through this week's top 10 shows for Ad Age (in the all-important 18-49 demographic, of course), and found that just 24 percent were sitcoms. Worse still, the average rating was a paltry 2.5. Only newsmagazines did worse. Reality TV made up 18 percent of the programs, but came out on top in ratings, with an average 3.6. Dramas cover almost half of the schedule and had a 2.7. (In case you forgot, a rating is a percentage of all TV households, whether or not their sets are turned on. For example, a 1.0 rating is 1 percent of the total U.S. households with a TV.) Rash says there's no "seminal sitcom," as in "All in the Family" in the '70s, "The Cosby Show" in the '80s, and "Seinfeld" in the '90s. But the problem is more fundamental. With few exceptions, sitcoms have lost their place in the interests of viewers, who seem perfectly happy to switch allegiances to reality programs (often a form of situation comedy). This is why the Writers Guild might have an rough go come contract time this fall. Reality shows are produced without writers - at least union writers - and the networks can easily thumb their noses at the WGA's demands because they have all the ratings cards, at least on the comedy front.