We re-wrote Learning Perl because I convinced O'Reilly and Randal to do it. They haven't redone Programming Perl probably because none of the authors have asked to do it as well as the fact that they don't need to do it.

Learning Perl covers 80% of the Perl that most people will use every day. It's a tutorial. Programming Perl, however, is the definitive reference. You'd have to stack three Learning Perl books to get the spine width of Programming Perl. They don't cover the same things because Programming Perl covers a lot more.

O'Reilly does have discounts for authors. You'd have to talk to them about using it though.