IMO, I don't see the problem here folks. I harbor no illusions of my being anything other than an amateur or hobbyist photographer. I may end up trying to shoot something to submit because I think it would be REALLY FRIGGIN' COOL to have a book cover credit to my name.
With all due respect to the other responders, maybe we can lighten up here just a bit. No one's "working for free". Payment has been stated as being cover credit and a pair of contributor copies. While that may not be a lot to some people, to some (like myself), published credit and being able to point to something and say, "I did that." or "I took that photo." may be worth more than anything. At the very least worth more than any monetary or tangible value. In no way does that undermine or devalue the work of ANYONE. Further, simply posting something like this has absolutely nothing to do with self respect or respecting an entire profession. If nothing else this could be an excellent opportunity for a photography student to get a legitimate credit to their name.
That being said, I would advise whomever submits to very carefully read through any and all agreements or contracts before actually submitting their works and etc.