It's easier to pirate music from a seemingly larger-than-life band than it is to pirate a book from a man who you (I, some of us?) watched grow the idea from a few blog posts a year ago. Perhaps I've got the narrative all wrong, but from my point of view, Mr. Kadavy made a couple really well-done blog posts covering "Design for Hackers", they became fairly popular on HN, he responded to comments on HN, got support for his book idea on HN, and made it happen.
Perhaps a better analogy is this: Yeah, I might pirate a Metallica song, but I'm not pirating the first album of that indie band I heard when I was passing through Louisville earlier this summer.