UPDATE: AppAdvice spoke to an Apple dev at WWDC and found out:

all of this was just a simple bug in the system. We decided to not just take their word for it, we tested all the possible scenerios we could think of and in all cases we were presented with the pleasant “You have already purchased this item. To download it again for free, select OK” message. We can confirm that repurchase option no longer appears in any instance.

Um, yeah, no. Although it's great that the restriction on re-downloading directly to the iPhone appears to be completely removed from iPhone 3.0 GM, the mere presence of the new dialog disallows anyone from playing the "bug" card. In any event, end users are now saved a good

ORIGINAL: Just over a week ago, TiPb reported that Apple had made a change to their re-download policy for iPhone 3.0 Beta 5. Previously, if you'd already bought a paid app, going to the App Store and hitting the Buy button again popped up a text alert saying you could download it for free.

With iPhone 3.0 Beta 5, which allowed for multiple iTunes account login, that message changed to "You can redownload it for free on your computer, or tap Buy to buy it again."

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We guessed this was to prevent app-sharing. If you logged in to 2 or more accounts, Apple didn't want you to be able to download your buddies apps free of charge as well. Not the best trade-off, but understandable.

Now AppAdvice has figured out more of what's going on:

In the final release of iTunes 8.2 last week, Apple included some logic that tells a device what iTunes accounts are authorized on the computer. Many users that were using the beta releases of iTunes were not prompted with an available update and found no reason to upgrade. Those users’ devices were never getting the authorization information to pass on to the App Store when they tried re-downloading apps.

So bottom line: if you have more than one legit iTunes account, authorize them all on iTunes 8.2 on your computer, then sync with your iPhone (running 3.0) and you should be good to go.

SInce we here at TiPb expect our buddies to buy their own apps anyway (and support developers so we get even more great apps!), that's just dandy with us.

(Thanks to Jay and Trevor for the tips!)