Witness this. I just finished reading Spring in Action a couple of days ago, the book was released "February 2005", and it's already outdated in this particular (small) area. This is exactly what SourceBeat is betting on -- being able to provide an up-to-date product throughout its lifetime.

No, I'm not working for SourceBeat and I much prefer reading my books from a dead wood surface, but I'm pretty sure there are many authors out there who'd love to put out a new print within a month of the original release.