Just read an article about a school librarian who has realized that the secret to getting her students in the library and excited about reading is to quantity not variety. Buy more copies of the titles they want to read, sometimes up to 10 or more. She's found that they are excited about the books, are in the library more, and tell her what books they like since she listens and does something about it.
As I usually do, I think about this concept in my own context or similar contexts. Could this work in an academic library? Could this work in a public library? Well, I think it already does in public libraries. Most public library systems I know buy multiple copies of the "bestsellers". But they seem to be based on more official definitions of such, turning to the NYT list or critics or whatnot. It would be interesting to hear about a system more like what this school librarian has done: becoming responsive to the wishes of the local users. Creating a community of communication around what is cool and what is popular.
And academic libraries? Well, unlike school and public libraries, a good portion of the information accessed in an academic library is not "for fun" or an "impulse buy". It's directed. They're looking up specific information or studying a specific topic often with a specific goal in mind, an exam, a paper, etc. They're not looking for what they want but what they need and what they need is easier to identify and quantify. There does not seem to be the need for a large quantity of single titles. There's enough variety in the goals of students and faculty most of the time, and even if there isn't, no one's coming in to access it at the same time.
There's also the e-solution. Academic libraries use more e-resources (ebooks, ejournals, databases, etc.) than public or school libraries. With e-resources, the option to allow access to more than one person at a time is almost a default and the cost for adding more "seats" is not usually the same as the first.
Also, a big factor in the reading habits of school and public library patrons is the popularity of material. Popularity, although a part of what is chosen in an academic library collection, is a minor part. In fact, many academic users are trying to do something unique to either set themselves apart from others or in direct competition to others.
[ Response to Give Them What They Want: Shake up your selection policy with multiple copies of popular books by Kristine Chen from the School Library Journal, discovered through my "collection development" Google News search feed ]