Hi Joe, I just read it! I think its a great article and so so clear and even with a source code sample.
I didnt test it but its autodeclarative (do this word exists? lol)
I'm, a ExEn developer and I think it even works with ExEn (exen.codeplex.com) because it uses monotouch inapp purchase.
If you want to improve your article, may be you can explain what monotouch classes do you use, what things do you assume you are using (eg: gamestateManagment and link it to XNA gamestateManagment sample). I understanded it because I use that stuff
in my game.
If you want to see my game, go to https://www.facebook.com/acomicofzombies
Greating from Argentina
PS: sorry about my awful english!