This same rule apples on Windows.
Since when was following Windows' example a good thing? There is no such limitations in macOS or any other desktop I'm using, and strangely enough, there are no problems with "unreachable controls", so I am curious on exactly how one would manage to move windows in a way so that window gadgets would really become unreachable. Anyways, I hope it will be possible to turn off this feature (IControl prefs), as my "amiga workflow" is very much accustomed to windows being limited by the screen border (and if I could request a feature, it would be to have another hotkey for grabbing and moving windows without having to use titlebar - then it would be possible to move windows in a way so that control gadgets would be unreachable.)
Tell that to my support team who regularly field support calls from users messing up and putting their window titlebars outside of a clickable area (i.e. off the top of the screen). There are "power users" (most users in these forums) that have a clue, and then there is Joe Average who would have no idea how to deal with a window bigger than the screen. These types of UI decisions are difficult - do you annoy the power users but keep the other 99% from getting into trouble, or do you make the power users happy but end up with loads more support calls and confusion.
I deal with this type of issue all the time in my day job, "dumbing things down" is a necessary evil if you want your support staff and costs to stay sane.