I’ll admit that this one’s grey area, but Apple posts data (about apps on the iPhone) on the public Internet. A user may wish to use that data in a more efficient manner, so they install an app to do it for them.
Oh, wait, they can’t, because that app is banned, because it uses that data that Apple has posted on the public Internet.
As the App Rejections blog points out, this is kinda screwy. Apple can’t stop screen scraping on the public Internet (robots.txt is voluntary, too,) but they own the iPhone platform, and can control anything that goes on on it.
Screen scraping is a valuable tool for getting at data when a site gives it to you in a form that’s not really usable to filter on that data. Sure, it’s sometimes abused, but in this case, it can only benefit users, and can’t harm Apple.
Source: App Rejections