Developer Fraser Speirs came across an unexpected iTunes dialog earlier today that could be a hint of a new, long-sought App Store feature: the ability to offer for-fee upgrades to apps, complete with discounts for those who bought older versions.
Up until now, App Store vendors have worked around the lack of a paid upgrade feature by offering different "versions" of their apps, but this has also meant there's been no ability to offer discounts to loyal purchasers of the previous version of the app, short of applying a temporary price discount to everyone and raising the price later on. Assuming this dialog box isn't a simple error (notice that it asks you to click OK, even though the button says Buy) and is an indication of the future direction of App Store purchases, it's indicative of far greater pricing flexibility for App Store vendors, and it could also mean the App Store won't be cluttered with old versions of apps that are no longer updated. Developers have been asking for an option like this since the beginning of the App Store -- it looks like Apple might finally be listening.
Editor's Note: Several commenters have noted that this dialog is also visible when you attempt to upgrade an app while logged into the 'wrong' iTunes store account, and may not actually signify the policy change that Craig Hockenberry wants to see.