As part of the ongoing sprucing up of the open source book line, they gave my first book (with Mark Stone and Sam Ockman) a new cover. Check it out. Also, the contents of this book are up on the internet if you'd rather read it that way. When we published it, there was no creative commons so some of it is released under the non-optimal (for text) GPL. I don't even think the GFDL was around then.
So, to join the chorus sung by Cory Doctorow, I think that the Book sold well likely because of the free nature of it. I hope Open Sources 2.0 (under a creative commons license) does as well....hell I hope it does much better :-)