It's interesting to juxtapose your excerpt from the HIG with megamark16's comment below ("When I click the Maximize button on OSX, it doesn't actually maximize the window 99% of the time, it just picks a seemingly random size.")
What this should tell us is that a UI strategy can be "optimal" -- in the sense that the HIG passage you quoted likely emerged from a lot of intense debate between some very bright, motivated people at Apple -- yet still unintuitive and confusing to users who weren't sitting on the committee that came up with it.
If we accept Einstein's dictum that things should be as simple as possible but no simpler, then it's very hard to defend the byzantine "Zoom" button in OS X. A sufficiently-complex model may indeed appear to be a random process to someone who sees only the model's behavior.
Adherence to convention is important, but so is quality documentation. I'd argue each of those virtues are on the downswing right now. Lots of new devs, faster platform feature additions, Apple failing to lead by example...pick three and add three of your own.
TL;DR: Put thorough doc under the Help menu. Every time.
Someone mentioned Photobooth hotkey weirdness below. There's definitely a (low, low) threshold at which the presence of mystery-hotkey functionality moves from "easter eggs yay!" to "your doc sucks." Dogcow moof was all the easter egg I needed, really.
The "apps should be obvious from first launch" maxim has had awful consequences here. Are people thinking "if it needs doc I did it wrong"? Because hey kids, it needs doc whether you think it's obvious or not.
Curious whether you'd consider this to be evidence of platform doc erosion:
I develop a pretty simple Mac application and market it through the MAS. It ships with thorough instructions that are available through the standard Help menu.
Aside from the odd feature request, the only question I ever hear from users (maybe 1% of them?) is: "I launched your app and it doesn't seem to be working at all. I went to your website and there's no PDF user manual to be found. Is it broken?"
My responses to that have morphed over time into a very polite text wrapper around a screenshot of the Help menu.
Are these isolated cases of people just not thinking to look for help under the Help menu, or has the overall quality of content under the Help menu declined to the point where a subset of users just never expect useful information to be there?
What this should tell us is that a UI strategy can be "optimal" -- in the sense that the HIG passage you quoted likely emerged from a lot of intense debate between some very bright, motivated people at Apple -- yet still unintuitive and confusing to users who weren't sitting on the committee that came up with it.
If we accept Einstein's dictum that things should be as simple as possible but no simpler, then it's very hard to defend the byzantine "Zoom" button in OS X. A sufficiently-complex model may indeed appear to be a random process to someone who sees only the model's behavior.