Apple claims jailbroken phones can crash transmission towers
macworld.com
macworld.com
If you've been following Apple's ongoing battle with the EFF, you can see what the real motivation for Apple's propaganda is: Apple has a series of tightly controlled revenue streams flowing through the iPhone, and they don't want that closed ecosystem threatened by the open source community. Movies, music, videos, applications, and other digital content connects the device directly in with their iTunes revenue streams and helps create a complete "suite" of products from Apple that users will be locked into purchasing.
Since the iPhone's release in 2007, developers have threatened that chain ... not with illegal pirating (although that's going to happen regardless), but rather with something Apple fears more than piracy: competition. The developer community has put together a complete community environment for the iPhone including Unix world, software repository, and even their own compiler and tool chain... and they did it long before Apple ever concocted their own. And developers distributing their own software are creating applications that can do more than AppStore apps, lending themselves to many times the number of sales that they'd otherwise get in the AppStore. That is at the heart of what threatens Apple, just as competing telco equipment was at the heart of what threatened AT&T back before they were broken up.
In reality, a jailbroken iPhone is no more unsafe than a laptop running an AT&T air card. In fact, a jailbroken iPhone runs more like a regular computer than one fresh out of the box. This all comes down to revenue for Apple and their bending over for AT&T. Apple will do anything, and say anything apparently, to protect that revenue stream from ever having to face real competition.
Anti-competitive practices are not even related to the case/issue of what they allow/disallow in the app store.