It really should come down to what the nature of the in-app purchases actually are, rather than the outlined concept.

I've been playing MS Flight recently, which is their idea of Free To Play.

More correctly though, about 10% of the game is free to play, giving your two aircraft and the island of Hawaii.
To unlock the rest of the Hawaiian Islands and get an additional aircraft: 1600 MSP
To unlock Alaska, 1200MSP
Aircraft range from 640MSP for a 'basic', meaning its only an external model and 1200MSP for a 'deluxe' one with a virtual cockpit.

This also extends to achievements which are, of course, further leveraged to encourage purchases. Of the 38 available, only 9 can be earned without paying for add-ons.
If you wanted to unlock all the achievements, you would need to pay a minimum of 4640 MSP for the Hawaiian Pack, Alaskan Pack, Maule M-7-260C and P-51D Mustang.
That's $58.

A $6.99 app with the ability to actually play through all of it is quite an improvement. :P