I find there is a strange mindset with the App store. Like on steam for example, if I see a game for $5 I think wow that is so cheap, I better get that. But on the app store, its like really expensive, even if it is the same game. I have nothing to back this mindset up other than general feeling and talking to others.
I also think the mindset if different with in-app-purchases, once people have been playing a game for awhile, getting 50 gems for $5 bucks seems more justified, in my mind anyway. Not really sure why this is, I guess there is a lot less risk involved, because you totally know what you are getting. That is why I am trying to go with the model of making it free, but selling level packs.