The headline is misleading. The base apps are free, but you pay for the full app via In-App Purchases. This isn't a whole lot different than the standard lite and full versions model.<p>How about the less-sensational: "One Third of Top-Grossing iPhone Apps Profit With In-App Purchases"
My favourite example is Billings (<a href="http://itunes.apple.com/us/app/billings-touch/id343938310?mt=8" rel="nofollow">http://itunes.apple.com/us/app/billings-touch/id343938310?mt...</a>). It doesn't sell content like music or in-game credits, but features. The app is free, but if you want to send invoices via email or sync it with your Mac, it'll cost you $14.99.