Why Did Apple Force Stanza to Disable USB Syncing?

TechCrunch reported that last night an update to the Stanza app appeared in the iPhone App store–version 2.1–with a curious change: Lexcycle, the company behind Stanza, which was bought last year by Amazon, had removed a feature from the app at Apple’s request. The App Store page for the updated version of Stanza said that the update “Removed the ability to share books via USB as required by Apple.”

Previously, Stanza users had been able to drag and drop books to and from the app on their iPhone using a USB cable. While many users probably never used this feature, as Stanza offers an in-app bookstore–others used it to sync ePub books bought from other stores to the Stanza app, like one user who anonymously complained about the update on Lexcycle’s user forums: “I guess I’ll never upgrade to 2.1 from 2.0 as this is how I get all my ePub books onto my iPhone.”

So here’s the big question: is this another example of Apple being too controlling of its ecosystem, or is it no big deal? It sounds like this Apple is requiring all App developers to disable USB syncing. Is this because they don’t want content they don’t know about making its way onto the iPhone, iPod Touch, and most relevantly, the upcoming iPad?

There’s already much worry about the fact that iBooks appears to be as closed a platform as the Kindle, meaning it looks like we won’t be able to bring eBooks purchased outside of iBooks into the app. Is apple now trying to prevent users from bringing outside eBooks into other apps too?