The fact that photobooks are given the same gallery treatment normally reserved for works of fine art is at least partial acknowledgment of the special role of the book in photography. There's no way such a show could be constructed around books of painting, sculpture, or multimedia. As many have commented before, photography has a special relationship with the book form, one which the artworld is just in the early stages of recognizing.
One hundred miles south of PDX Gallery is another photo show which for many will be worth the drive. Eugene's DIVA Gallery, not normally a hotbed of daring photography, is currently showing Rhapsody in Black and White, a collection of photographs by Charles "Teenie" Harris . Harris spent his photographic career (roughly the 30s through the 60s) at the Pittsburgh Courier documenting all aspects of Pittsburgh's black community, amassing a collection of 80,000 images now housed at the Carnegie Museum of Art. About 30 of these are on display at DIVA. The photographs are documentary in the strongest most beautiful sense of the word, opening (at least for me) a mental window into a world I hadn't thought much about. There is a raw reality to these scenes which permeates their core, and which provides relief from the current trend in photography toward conceptual/staged/manipulated images.