I doubt it had anything to do with the safety briefing and more to do with the fact that it was a "carryon" and the FA wanted it stowed. When I work A Position I don't allow anything to be held in the lap for takeoff and landing, the also includes the area at your feet, behind your feet etc. I used to not worry so much about it but then I had a rejected take-off due to engine problems and the force of the braking sent a purse right into my stomach (I was sitting FWD Jumpseat Aisle-Side)... and now I can see WHY the FAA says everything must be stowed at row 1.

As for the book, if it were a small book I don't think it'd matter, but if it were one of the HUGE Harry Potter Series then I might ask to have it stowed.

...again, this is only for takeoff and landing, hardly an inconvenience.