Originally Posted by Kali Yuga
In addition, what works for O'Reilly may not work for others. They're happy to write off unauthorized downloads as a type of promotional cost. Meanwhile, O'Reilly pays a low royalty rate (10%) aren't reimbursing authors for possible "lost sales," and has a tech-savvy and sensitive audience. All of these are factors largely unique to them and their business model.
Also probably a customer base where a reasonable proportion of the sales are corporate. Why go out of my way to get the free version if I'm not paying for it anyway, my company is?