Technology impacts every industry and publishing is no exception. This article from TheBookseller.com asks whether "out-of-print is outdated." The short answer is yes, for the most part.
Publishers do indeed want to hang onto and exploit rights for as long as they can, especially as they're building out more of a digital presence. Most also figure they made a significant investment in the project and they'd like to enjoy the long tail revenues for as many years as possible.
I agree with that logic and apply it to my own group at Wiley, but I'm also a reasonable person. If an author figures they can do better by placing the book with another publisher (or self-publishing it) I'll generally do what I can to revert their rights. I say "generally" and not "always" because there are plenty of factors to consider. For example, where are we in the life cycle of the book? It might be selling a modest quantity every month and we've got plenty of inventory on-hand; we, the publisher, invested in producing that inventory and I'd like to recoup as much of that investment as possible. But when sales go negative (returns exceed gross sales) or we're down to single-digit sales over several months, well, that's a pretty good sign that the book has run its course.
The big question authors need to ask themselves is the one Derek Johns asks in this article: "...where else can you go?" Is another publisher really interested in taking this book on as a new title? If so, why? That's important information to share with the current publisher -- it's a bit of a long shot, but maybe the current publisher could use that information to spark renewed interest and sales of the book without having to change publishers.
At the end of the day, if you (the author) feel like you'd be better served by getting your rights back, give your editor or publisher a call and have an honest discussion with them. Regardless of what your contract says, exceptions can be made. I still tend to think you're better off letting the current publisher do what they can to push the book as part of their backlist, but like anything else, it's best to talk it through so that you thoroughly understand the pros and cons.