Late yesterday Lendle received a response from Amazon explaining why they were cut off. Lendle didn't share the complete details, but they did tell us something:
Late today, we received an email from an Associates Account Specialist at Amazon informing us that their concern only relates to our Book Sync tool, which syncs a user’s Kindle books with their Lendle account. Amazon informed us that if we disabled this feature, our access to the API, as well as our Amazon Associates account, would be reinstated.
So it looks like I was right, and Lendle did something specific to piss off Amazon. Everyone who got mad at Amazon for attacking a lending site was wrong. This is an example of why you shouldn't jump to conclusions. Amazon didn't do anything to harm most of these lending sites, only the ones that probably broke a rule.
I don't claim to understand the technical details, but a number of readers on my last post about Lendle reported that Lendle did more than other ebook lending sites, and there was a chance that Lendle did break one of Amazon's rules.
One commenter was a developer who had worked with Amazon before, and he thought this was how Lendle violated the rules (thanks, Michael):
Last I checked, there was no way to access a Lending Enabled attribute through the Product Advertising API. If a web service needs to confirm a title’s lendability, then I’m unaware of any way to do so aside from scraping the HTML from the actual product page. This is strictly verbotten in dealing with Amazon. The whole reason for offering an API is to control how data is accessed (and also to varying degrees, how it is used), and any registered developer accessing Amazon.com in an unapproved manner would definitely be putting their continued use of the API in jeopardy.
If he's right, then you really can't blame Amazon for cutting off Lendle. This was a perfectly valid reason to do so.