After playing with iPhoto for a bit myself, I will agree with Lukas Mathis, especially since the iPad and iPhone versions are somewhat different, too. GarageBand and iMovie suffer from this at a lesser extent, but once you get the hang of the basics, the apps feel intuitive:
It’s okay to have a few gestures that aren’t easily discoverable, if they are simple, universally applicable, and fun enough that people will teach them to each other. Pinch-to-zoom is one such gesture. Most people probably won’t discover it on their own, but it’s such a fun gesture that the people who know it will show it to those who don’t. It’s also easy to learn and remember, and it works pretty much everywhere, so pinching pictures quickly becomes second nature.
Unfortunately, iPhoto’s hidden gestures aren’t particularly fun, and they only work in iPhoto. iOS’s built-in «Photos» app is a completely different application, despite doing essentially the same thing as iPhoto, running on the same device, and coming from the same company. Almost nothing you learn in iPhoto can be applied to Photos, or to any other iOS app. In fact, being proficient at using iPhoto will probably make you worse at using Photos.