DRM doesn't come cheap, so developers likely want some assurance that the headaches and PR issues it can cause are at least offset by a drop in piracy rates. The study, which polled people in the industry for several years, unsurprisingly concluded that any DRM technology ultimately will work to restrict legal use of content. The reason seems obvious; it's impossible to predict in advance all the potential legal uses of software, so invariably some are bound to find themselves cut off.
The study covered some grey areas of copy protection, such as users wanting to duplicate or rip their own content. While you may be suspicious of claims that DRM inherently breeds piracy, as there are too many factors to make such a statement, the study did come to one conclusion that many can agree with. As a whole, DRM technology doesn't appear to be doing anything to stop piracy. Of course, many of us could have told them that without spending years studying it.