Simple sales strategy - marketers place items in the special island displays at the entrance like Barnes or at eye level in grocery stores to encourage impulse buys. They are items that are new or that don't have reliable sales figures. Thus, the consumer needs to be tricked into buying.
However, a product that the marketers know has a guaranteed sale are placed out of impulse reach - the bottom shelves in a grocery store or back on the regular subject shelves in a book store. The customer enters the store already intending to buy this item so no impulse lure is required.
Essentially, pro-Bush books have a guaranteed, regular demand resulting in steady sales so no special marketing tricks are needed....just like tomato soup.
Very possible true. But you forget one little tool that the marketers use in the grocery stores that that affects product placement and just might also be applicable in book stores:
Slotting fees.