They will indeed serve any random ebook. However, it comes encumbered by DRM (thus controlled digital lending) and they "own" an instance for each copy they len

They will indeed serve any random ebook. However, it comes encumbered by DRM (thus controlled digital lending) and they "own" an instance for each copy they lend at any given time (hence the waitlists they refer to). Note that many other libraries across the nation engage in exactly the same practice. Of course the legal problem is that digital goods are "licensed" instead of "owned" ...