Just think, if this were a game for Nintendo DS or PS Vita it would be $30-40. And if it were for the consoles it would be $50-60. $6.99 is a steal for mobile gaming.
I think IAPs are great for one purpose - to allow one to try an app or game free before buying it. Eg: a game with 50 levels - first 5 are free, so you can see if you like it; IAP to unlock the rest. Or a game like Trivia Crack - put an ad in the app, but otherwise keep the app playable; if you like the app enough to want to remove the ad, then IAP. Though, TC does have other IAPs, but the ad-removing one is the only IAP I'm likely to use.
For non-games, I've seen similar smart use of IAPs - a todo app that allows you 10 items, but IAP to unlock unlimited tasks - that way you can freely try it out before committing money to the app.
In a perfect world, though, free app trials should be allowed.