Reading the Classics - Scrolls etc.

Debra Hamel, of the Blogographos Blog, mentions an article on another blog ("Reading Under the Covers") on prisoners reading the classics. The Reading Under the Covers blog displays a painting of philsophers holding a book. The blogger objects that in ancient Greece the philosophers would have held a scroll. Is the article in question actually (anachronistically) a bound book? Could it not be a wax tablet as in this modern replica?