Given the danger a small, dense object represents in an accident, that alone is sufficient reason to require that people put the things away.
For those who feel that hardcover books represent a similar danger, try the following experiment:
- take an open hardcover book, throw it as hard as you can at a wall 6' away, observe the size of the dent (if any) which it makes
- repeat that w/ some small electronic device, compare the relative size of the damage
http://abcnews.go.com/GMA/story?id=128062&page=1
William