I think ebooks are relatively safe from piracy.
the problem is that downloading a pack of 700 MB,can easily get you 700 books,compared to only 1 movie.
the slides talk about availability of pirated copies in terms of seeds and leechers, which implies that they're only looking at Bittorrent, which may not be a very good measure of availability
It indeed is not. Seeing 30 peers, 60 leechers can mean 90 illegal downloads the whole day, or, it could also mean lots of users downloading and closing their upload as soon as they have their ebooks.
There's just no way of telling.