Yeah, I see your point about the cover of a book being more like a piece of clothing than an ipod. Makes sense that the fact that it was at work, rather than in public, would factor in as well.
What strikes me even more than the ruling is just the fact that someone would complain about something like this. If that kind of thing is so offensive to you that you feel the need to make a complaint, how the hell do you get by in the outside world? Most of us see or hear something that is very offensive on a fairly regular basis. If these people are really this sensitive, they must find themselves damn near in tears every time they turn on the TV or walk by a frat house on a Friday night.
Of course it's possible that they are just complainers. I think we've all worked, gone to school, or otherwise dealt with this type of person at some point. People whose need to complain is so strong that they will go out of their way to be offended just to have an excuse to bitch. Obviously I don't know anyone involved, so I can't really judge, but my guess would be that this describes the complainers in this story. These people can be pretty terrible to deal with.