I really disagree with your first sentence. A few of the icons are obvious, but most are extremely vague. I actually use a Mac every day at work and I can't tell you what half of these icons are for (I guess I don't use them). For example the rocket icon, the book (is it a reader or a dictionary or what?), Safari's icon looks like a map app since it's a compass.
I don't know what the history/clock icon is for and the app store icon is just terrible, and has even fewer context clues in languages where the word "app" doesn't start with a Latin A character.
Icons rely on all kinds of assumptions and cultural cues. They might as well be hieroglyphics to people who aren't familiar with them, which is why they need to come with labels or tooltips.