That's behaviour that's been around since Windows 3.1. There used to be a little menu there with a few options and if you double clicked the icon it would close the window.
Heh, yeah the context menu on the scroll bars is my go-to tell to discover whether it's a real scroll bar widget or an imitation one. (Gotta write an article on that too one day)
Yeah, I like that too. Makes you think twice about re-implementing widgets because of the insane amount of functionality that is tied even to the simplest widgets and still invisible.
Think of how hard it would be to re-implement a dropdown, for instance: You would need to implement keyboard navigation (arrow keys), jump-to-entry (using the letter-keys), srolling with the mouse wheel, flipping through entries while the dropdown menu is closed and probably a thousand other things that I never used but some people do.
I did do this back in the VB5 days and it was a proper pain. From memory I couldn't get the listbox window to draw outside of it's hosting window (needed for controls at the bottom of a window) and allow moving of the hosting window at the same time.
In the end I think I cheated and drew the list box on the parent with an option to go up or down depending on it's relative position.
>context menu on scroll bars - no idea who would use this
It is for accessibility. Alternative input methods, like emulating the mouse by keyboard for instance, might not have mouse-drag functionality, but will have a right-click function.
Is the menu still there on all the apps? So the icon is missing, but the menu opens up? That's brilliant. Haven't used Windows for a long time but every time I do I'm still amazed to find that close behaviour still works.
The link I posted above links to another one with more historical context. I'd never clicked that the icon was meant to look like a space bar.
http://ux.stackexchange.com/a/55261