Books get published, get read and then go out of print. You then end up trawling second hand bookshops and these days the internet to track down a copy at a reasonable price. And of course publishers are faced with the costs of warehousing the inventory, something that's increasingly expensive, so the old, the obscure, and the plain boring end up being dumped onthe second hand and remainder market really early, or if you're unlucky, pulped.
Some university and academic publishers have gone to a print on demand model, where the text is prepared for printing and copies are only printed as one offs as required, which in these days of cheap high volume laser printing is a really compelling way to go - no warehousing or inventory management costs.
Now comes news of Faber Finds - a mainstream UK publisher giving print on demand to its back list - basically you get a bound printed copy of a book from the back list on request. Of course this costs money, but it does provide an interesting change in the way of providing access to out of print texts, and incidentally to scanning and digitally archiving these books.