I think one of the effects we can observe here is cognitive dissonance. If people pirate a book or a movie or an album they like but did not pay for it they will have to cope with cognitive dissonance. A lot of people with then buy the book they downloaded to 'make up for it' and/or will as Neil suggested buy the future books of the newly discovered author.
The web is a great place to discover new things and it seems that Paul Coelho and Neil Gaiman really see the upside of having their works out there on the web for free and embrace it.
Cognitive dissonance is a discomfort caused by a conflict of two cognitions. In this case 1) "I like this book" and 2) "I did not pay for that book even though I should have".
Now there are a few ways to resolve with that dissonance. A way to do that is to change one of your cognitions, you could 1) tell yourself that the book wasn't good at all and therefore not worth paying for, or 2) pay for the book because you liked it - either way you eliminated the controversy.