I seem to recall Steve Jobs saying the reason the menu is at the top of the screen is that it's easier to hit it with the mouse, you just push it all the way up. I think it's a valid point.
I've noticed it's really nice if you like quarter- and half-screen layouts (or anything else that's sorta tiling-like). Four different programs on the screen, only one "file, edit, ..." menubar eating space.
Apple's HIG used to have a bunch of these nuggets - things about predictability of where inputs are, what was clickable, etc. Not sure how much has been preserved over the years, but the original docs are pretty legendary.
One nice thing about this too is that when you have something like a full-screen video playing, pushing the mouse to the top of the screen will reveal the menu pretty much universally. Trying to get to the application menu in full-screen on Windows is going to vary from one app to the next and has poor discoverability.
At the same time they don't utilize the 4 most easy to reach points of the screen, the corners. Windows always used those for essential interactions so the interface was really fast to use: for the start menu just throw your mouse to the bottom left corner; to close the window throw your mouse to the top right corner; to show your desktop throw to to bottom right; not sure anymore about the other corner as I am on Mac for a while already. Since switching to Mac I am always thinking about how stupid the interface is for disregarding important user-friendly details like these.
Apple has Hot Corners (configurable in the Desktop & Screen Saver > Screen Saver section of Settings) that can replicate some of the functionality that you described.
I have had my second monitor on top of my main one for the last 20 years, when I switched to a Mac this was the hardest thing to get used to.