I think it somewhat depends on the library’s collection, but overall you’re right. I think a big thing is the feeling of scarcity. If you decide not to buy something at a chain store, you can expect it to be there the next time you’re there. The same is true of the library, though you may have to wait for it. At a used bookstore, that may be the only copy that ever comes into that store. If you don’t buy it and don’t write down the name/author, you may not ever be able to find it again.