Earlier quoted context omitted.
Now how do I do this with a mouse? (I already know the answer, but I'm curious if you do. It isn't very discoverable.)
Drag and drop from one folder to another is how I would do it with a mouse only. Is there another way?
If you want to copy a file in OSX with your mouse you use the menu bar whereas if you want to cut and paste (move) a file in OSX with your mouse then you use the two open windows method that you describe.
They are both very different and one isn't so discoverable.
What's the worst about this is that it's purely a choice and Apple intentionally greys out the cut option in the menu bar.
Madness.