To me, there's a distinctive difference between adding a non-audible watermark to a audio file vs. watermarking text with text. I can listen to purchased iTunes music all day long and never even be aware of the watermarking existing, but I can't look at a single page of my [one and only] Packt Publishing ebook without their giant logo, my name, date of purchase and my address being displayed in the footer.

If they wanted to watermark my info into the file to prevent file sharing, that's fine. Printed on every page? Obnoxious. It's another case of legitimate purchases having a disincentive that piracy doesn't. I bought the book, I know I bought the book, I don't need to be reminded 272 times in the process of consuming it.