I can understand cromag's concern. While there may be no legal liability (as the books in question are free) there is still the moral question. I know I wouldn't want someone just feeling free to post my work where they please without my knowledge. What's to stop someone from claiming that it's their work and not mine? And what's to stop them if they buy a copy of the work that does cost $ and start selling it? Even if they just post the one that costs $ for free not only would income be lost but what would stop someone from adding it to a torrent file? Granted it sounds like they have only posted the free books so far, but it could be a slippery slope.
Assuming they honor those requests I'd still be wary about providing my email address to someone with such a convenient sense of honesty -- I don't really need more spam in my inbox.
Avoiding spam in your inbox should be easy cromag, just open a new email account just for such concerns as this.