LCD
This was Air2000 back in the day. I'm not sure if their policies have changed since the merger with Thomson.
I think it's a perfectly valid theory that a book (a heavy, hardback book) could be a projectile at an exit row with no bulkhead. At ordinary seats there is the seat in front to block it's path. There is not much except the crew members face opposite to block a flying book at an exit. After that, what happens to the book. It's sliding on the floor in everyone's way.
The other consideration is bracing. What do you do with the book if you have to adopt the brace position. How many valuable seconds are wasted trying to find a secure place for it? Where will the book end up?
I'm also SCCM (currently on unpaid leave) and have spent time in SEP training and recruitment. I've flown for 7 airlines plus 5 'host carriers' - under 4 aviation authorities. All have differing standards of SEP and different standards in the everyday onboard situation. Air2000 is the only airline I have flown with that is this strict and have complusory debriefings after every flight where SEP infractions are addressed.