alt Hacker NewsThe problem with the Mac UI is that the app's menubar can only be accessed by the mouse (can't remember what accessibility-enabled mode would allow).
Under Windows, one can access the app's menubar by pressing the ALT key to move focus up to the menubar and use the cursor keys to navigate along the menubar. If you know the letter associated with the top-level menu (shown as underlined), then ALT-[letter] would access that top-level menu (typically ALT-F would get you to the File menu). So the Windows user wouldn't have to move the mouse at all, Fitt's Law to the max (or is it min? whatever, it's instant access).
For the ultrawide monitors these days (width >= 4Kpx), if you have an app window maximized (or even spanning more than half the screen), accessing the menu via mouse is just terrible ergonomics on any major OS.
Since OS X 10.3 (2003) Control+F2 moves focus to the Apple menu. The arrow keys can then select any menu item which is selected with Return or canceled with Escape. Command+? will bring you to a search box in the Help menu. Not only that, any menu item in any app can be bound to any keyboard shortcut of the user's choosing not just the defaults provided by the system or application.