This was almost as big a gaffe as the Bud Light fiasco, just one that effected a smaller group and not the general public. Unity really messed up.
I actually started working on a little Unity project as a hobby a couple months ago, and after this happened I am glad I was only a little ways into development because it will be simple to rebuild it on another engine.
They might have gotten away with a penny per purchase, and still made a ton of money.
The problem is that they want to keep charging people for something they already bought.
I actually can see their view, but they certainly messed up on the implementation.
In order to continue to fix bug, make new features, etc.. they need to be able to employ people.