So Amazon recently changed the terms of service for their Product Advertising API, which is in use in applications such as Delicious Library. This is (I believe) the API by which DL gets its book information, and through which it provides links to related items, reviews, etc.
The new license includes this marvellous little tidbit in section 4e:
"You will not, without our express prior written approval requested via this link, use any Product Advertising Content on or in connection with any site or application designed or intended for use with a mobile phone or other handheld device."
It remains to be seen whether Amazon will eventually grant an exception to its policies, Shipley will find another source for the necessary data, or if the iPhone version is truly gone for good.