Actually, the motivation behind the project stem's from Dan's stay in Russia before his graduate studies.
He realized that their are tons of old posters, pictures, and other soviet propoganda floating around the country's libraries that many people in the western world would like to view, but are unwilling to go to Russia to see.
He wanted to digitize some of these posters (works of art, in his view) in order to circulate them on the web. He soon became very frustrated with using a flatbed scanner, and stopped.
Zoom ahead a few years later, Instrucatables is having a contest to win an epilog laser cutter, so he decided to build a book scanner out of recycled (read: trash) materials and submits the project, and wins. He says he's surprised at how well the project has resonated with the web community.