Dan Moren has it absolutely right here.
The App Store, you see, has very strict rules on pricing. Among those is “no paid updates.†It’s an all-or-nothing proposition: either every upgrade to an application is free for everybody, regardless of how much work the developer puts into it, or the upgrade is delivered as a “new†application that everybody has to pay for it. There’s no facility—none—for developers to give some customers a break on a upgrade price without sending each and every one a check for the discount.
That said, three bucks is still a more than reasonable price for Tweetie 2, even as an upgrade.