I think that's different. In arcade's example, the only reason you needed a coin is when you have used all your lives. Now, if you had better skills, you could get through the entire game without a single additional coin.
In IAP module, the game is designed so there is no chance (at least for 99% players) to go through the game without purchasing the stuff on the go. Take "where is my water" for example. You can continue game as long as you keep scoring all 3 coins on each level. If you miss even one coin, after many levels you will be missing that coin to open another level. There you have an option to open the level for $$$ Now, some of those coins, in my gaming experience, were impossible to score, but that's a different story...
Some modern shoot-em-ups in the arcade have blatantly unfair portions of the game where you WILL get hit and lose a life. See CarnEvil for an example. I would consider these similar to IAP.
Older arcade games like Galaga and Super Mario Brothers, however, give you a fair opportunity to avoid the "Insert Coin to Continue" screen based on your skill. I can last 20-30 minutes on a single quarter easily for both of those games.
