I saw some tweets when it was first announced and I wasn't sure why folks were carrying on really.
Why would a book made with iBooks Author that's only compatible with the iBooks app be available for other devices? If I used Amazon's Kindle creator program, I wouldn't expect the book to be used on the Nook or in the iBooks app (or Stanza or Kobo, etc.)
Yeah, I think one of the two main concerns so far, and the one that really bothered me, was the question of copyright and ownership of the actual work, and this seems to stem from confusion over the EULA wording. As I understand it now, and as the quote you posted seems to confirm, Apple only claims ownership of the .ibooks file that you produce - not of its contents per se, which makes it much easier for me to swallow. The problem I saw was that they would presumably own the written work of submitters, while at the same time claiming no liability to loss of profit, even if they decided not to publish it or make it accessible at all.
That said, on the issue of exclusive availability through the iBooks store, they might still have some legal issues as per this article