The medieval manuscript served many functions above and beyond those of the modern book. It not only transmitted information and cultural values in a variety of fields, but it also served as a valuable objet d’art itself. Books could have incredible wealth and value and at one point were well beyond the means of the average person. The creation of religious books glorified the patron as well as God, whether the text was a private devotional, like a book of hours, or a text for mass display and worship services, like a psalter. Other works served a practical function and contained chronicles of rulers and medical texts. Despite their functional variety, all of these manuscripts shared a common history and origin of production.
One of the key ideas here concerns avoiding a modern attitude to "flatten" the book to mere transmission. Surely the author means to speak more of illuminated manuscripts than rather plain-set codices such as the Exeter Book. I can't imagine conceiving of Exeter as an objet d’art, but I think we can fairly say it served an important role as a single star in a universe of knowledge.
It makes me wonder about the tenth-century libraries of some of the great centers of learning in England. I'll have to do some digging and see what I find.