Nope, that's not obvious either. Also a result of convention.
Also, even if people didn't understand the traffic light metaphor, a quick mouseover would clear it up: if you hover over the red button, it turns into a (X), if you hover over the yellow button, it turns into a (–), if you hover over the green button, it turns into a (+).
'Cat, Dog, Rabbit' makes sense, 'Cat, Sonic boom, Carpentry' does not.
"Your app determines the initial size and position of a window, which is called the standard state. If the user changes a window’s size or location by at least 7 points, the new size and location is the called the user state. The user can toggle between the standard state and the user state by clicking the zoom button in the title bar. Follow the guidelines in this section so that users can have the zoom experience they expect."
https://developer.apple.com/library/mac/#documentation/UserE...
True, they make no sense. A Mac user who has never used Windows will not understand them. On OS X, the buttons have the colors of a traffic light (red=close, yellow=minimize, green=zoom). Windows users trying a Mac for the first time understand this instantly.
"They have become a standard since roughly the days of Windows 3.1."
No, Windows 3.1 had different buttons [1]. The 'standard' you're referring to was introduced 3 years later, in Windows 95.
"We expect them to be there, and I prefer the icons to a little status bar that says "Minimize, Restore, Close.""
Sure, you can get used to anything, just like you can learn what math symbols and traffic signs mean. That doesn't make it intuitive, quite the opposite.
"Consider a recent example - the share icon"
There is no such thing as 'the share icon'. Looking at the Google Image results, there are tons of different icons that are supposed to mean 'share'. If there is one share icon that I see a lot, it's "arrow jumping out of a window frame" [2].
"Let's consider that it might actually be important to push new icons into the public icon lexicon."
Sure, but that only works if everyone implements them and even then, those buttons will need to be accompanied by text labels for at least five years.
[1] http://www.microsoft.com/typography/ttfinst/ttfinst8.gif
[2] http://bit.ly/10IELWe