To continue using the iPhone as an example, I realized that after two years, my Dad never realized that double clicking brings up the app switcher. I agree that it is better if you don't need a walkthrough, but I wouldn't say that you "blew it" if your app needs one. If a 30 second tutorial let's the user do very powerful and intuitive things, things that may save the user time over the long run, than maybe it is okay.