I think you're kidding yourself if you believe that you can describe what an app does with an icon.
Don't tell that to Apple.
Many of the references are obscure, but not non-existent. How about the Safari compass? The gears of Settings? The face on the Finder? A hammer and blueprints?
The Photoshop and Adobe reader icons are not descriptive.
I'm not saying that being descriptive is impossible or should be avoided. I just don't think it's the most important thing. Most of the time you can only get the reference to what the icon is describing after you know what the app does. It's not really a discoverable feature.
Maybe different people are different about this. I never paid attention to the meaning of the Safari compass before this minute. I guess there is a kind of descriptive meaning there but it never impinged on my consciousness for the past nine years. It still served its function of helping me to find that app among other app icons though.
A number of the apple app icons are basically screen-shots of the app. Terminal, Console, Spaces, Activity Monitor. You only get the reference after you've seen the app.