Hi KGill,
I STRONGLY disagree with this notion. Everyone should have the right to develop an app no matter what platform. Of course Padrucci is being sold to consumers, are you saying that developers cannot create their own IMSLP apps as well? If I remembered correctly, IMSLP.org is under the following license
http://www.gnu.org/copyleft/fdl.html. I'm sure 'profit sharing' is involved with the Padrucci app.
In terms of usefulness, why would it be useful to have one app. Maybe a developer has a different way to approach a problem or present content. Obviously the Padrucci app exists, that doesn't mean it has to be the only one. Padrucci shouldn't be the only IMSLP to 'monopolize' the content of IMSLP. And besides, it's up to the users to decide what app to purchase, let them choose.
Think of it this way, if one app crashes, why not try the other? Useful to have choices for sure.
Although Padrucci is the 'first' app to hit the store, doesn't mean it has to be the ONLY one.
Keep on going Alfred.