Upgrade Pricing Now Available on the iOS App Store?

I was looking at a crossword app that I use today, and saw that there was a new version. I downloaded the free version of Crosswords, and still had the older version – Crosswords Classic – on my iPad.

When I launched the app, and tapped on one of its menu items, I saw a dialog asking if I wanted to upgrade, saying that, since I had purchased the previous version, I was eligible for a reduced price:

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I went ahead, and was told that the price of the upgrade would be an in-app purchase:

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So, instead of $10 for the new version, I was able to buy it for only $4; an upgrade price.

I have never seen app upgrade pricing on the iOS App Store. If this is new, I’ve never heard about it before. If it’s not upgrade pricing, then the developer figured out a neat loophole to offer upgrade pricing through an in-app purchase. Perhaps the app noticed that I had the previous version on my iPad; or, it simply knew I had purchased it, somehow.

Could this be an early example of iOS App Store upgrade pricing, which Apple will announce at the WWDC tomorrow? Or is it just a smart developer who figured out a way to offer upgrade pricing? Has anyone seen this before with other apps?