I've been looking at the store too.
As far as prices are concerned, they seemed to be all over the place. Some books are very expensive, others are not too bad. And I believe that in most cases, it's the publishers who set the prices.
Looking at the Jodi Picoult books, it looks like the author has sold books to many different publishers (in BooksOnBoards, I saw HarperCollins, S&S, Penguin...). It seems that in AU/NZ, the books are published by Allen & Unwin (an Aussie publisher), who don't seem to be noted for the reasonable ebook pricing
Selection: It seems that of the "Main" publishers, RedGroup have only got a selection from HarperCollins and Random House so far.