As far as I remember, for the past 3 years, every app put into those stores by Apple themselves received unlimited upgrades.
Everybody wanted to do paid upgrade, pressuring Apple into adding some paid upgrade feature into the store. Apple always declined, saying "do as we do, support unlimited upgrades, you'll earn enough because the market is growing".
Some devs did paid upgrades by creating a new app with a new name, creating some issues along the way (people that just bought the old version a day ago have no upgrade path etc.) Not idea.
People guessed that Apple would add some "paid upgrade" feature once they needed it themselves.
Now Apple decided for the first time to create a paid upgrade, and apparently they - just created a new app...
For many people, a DAWs are used on real "workstations" in music studios. In that environment, the software and hardware are all bought once at the start, and don't get upgraded until the computer is obsolete. (It's mission critical... you wouldn't update AutoCAD or even MS Office if there was a risk something would change. You also have to retrain everyone in your studio.)
I believe that this is a new item though. For example, usually you can see the reviews for the previous versions in the app store but there are no reviews for Logic X.
