Publishing under free software license is our big motivation.

And, in fact, pragmatic reasons we have:

• we can use very-very various libraries under GPL to improve our application
  
• we can expect to learn more efficient code from derivative products

"Can we re-produce source code reader with this code in AppStore?"

"Yes, of course". Under GPL, you can do it with providing your own code. We cannot prohibit that in any way.