[kcase]

I agree that's a valuable, long-standing practice, but that problem has been solved: by offering discounted in-app purchases, we've been offering upgrade discounts to upgrading Mac App Store customers since we shipped OmniGraffle 6 in 2013.

If you read my latest blog post on the subject (linked in my first comment in this thread), you can see full details on how we're offering upgrade discounts to all existing customers, free upgrades for recent purchases, and free trials so new customers can check out the app before they pay—all in the App Store.