Why Are Classic Novels Cheap On iTunes But Not On Amazon?

I've noticed some famous, classic novels (in e-book format) available on iTunes at prices you normally expect from old books in the public domain, yet I'm not sure that's the case with any of these. And I see no attempt at price matching from Amazon Books. And the prices of these books on Barnes & Noble's Nook bookstore are in line with Amazon. Are all these English versions from different publishers on iTunes legal, I ask myself. Hmm.

For example:

Fahrenheit 451 by Ray Bradbury (1953)
iTune...