First, the sudden implosion of Borders left a large hole in the market. While Borders was not financially sustainable they still had a few million customers at least. It is reasonable to assume that those customers migrated to other stores when Borders closed. The same argument can be inferred from Barnes and Noble's slow death. As B&N closes a few stores a year we see a migration of customers to other stores, which artificially inflates those stores numbers and may be creating the sense of viability and health that we read about for indy bookstores. What we really need are demographic breakdowns of those customers to see if bookstores are capturing a large enough percentage of new and young readers to remain viable for the long term. I for one am not convinced, as I live in a very rural and slow adopting community that is generally 10-20 years behind broader American society. For example, I have never seen a community where so many private businesses do not have a website, and many are consciously choosing not to get on the web. But even in our less tech savvy community the local and privately owned bookstores are struggling to make ends meet.
While I hope that bookstores survive another century, I cannot feel as certain as others that they will.