This article was written by a publisher, O'Reilly, and they are obviously against copying. They don't use DRM because they know that it simply doesn't work, it would be a wasted effort, and as a bonus this way they can look "free", "open" and "cool". Of course they use the words "copying" and "theft" interchangeably, they don't really know or care about the difference, they are just bullshitting.