American readers are clustered into nearly disjoint groups. According to this kick-ass study (I found the link on boingboing) Americans can be split right down the middle according to the books they read. More precisely, they studied data from online retailers to determine which pairs of books were most frequently bought in the same transaction. They found two separate groups of books. The first groups contains such books as Crashing the Party, Stupid White Men, Manufacturing Consent, and The Bush Dyslexicon. The second group contains such honored titles as Fighting Back, Why We Fight, and Hell to Pay. They made a graph:

People who read from one group apparently don't read from the other. Most of my reading choices obviously come from the first group. I've never heard of most of the items in the second group. But I have checked out some of them, and I propose this explanation for why the groups are split: group two is just rock-stupid. The study's author suggests the following:

It appears that echo chambers have emerged that repeat a consistent message within each cluster. Ron Burt, a leading network expert, explains that a tightly closed network "amplifies predispositions, creating a structural arthritis in which people cannot learn what they do not already know"[PDF...]. With no direct bridges between the clusters, these divisions are unlikely to change any time soon.

I think there's a simpler explanation: group II books are beneath group I readers; they simply don't offer any intellectual value (Bill O'Fuckin'Reilly is in group I for Christ's fuckin' sake). Group II readers simply don't have the mental equipment to process the selections from group I. I realize that my explanation is impolite, but I think it is probably correct.