How to update Mainstage

Hello.

I bought Logic Studio 8, and when apple updated it to Logic 9 I bought the update. After that, Apple decides to sell Logic and Mainstage in the AppStore. I have some issues with Mainstage, ´cause my son is using it to play piano, and I want to update to Mainstage 2.2.x but I don´t find any way to do that, Have I to buy the new Mainstage version in the App Store?... I think it is stupid, but I don´t see other solution....

Thanks all for your comments...