Right Alt doesn't exist on all keyboard layouts. On the UK layout it's replaced by AltGr, which doesn't do much appart from fail to act as Alt for Alt+F4 purposes, but it has actual uses in other layouts: https://en.wikipedia.org/wiki/AltGr_key
Nobody ever uses right alt even if it exists, but it's straightforward to hit F4 with your right hand.
Alt+F4 on Windows has the undesirable property that if you hit it several times, and it works, you'll close several different things. Ctrl-C in the terminal won't do this.
American Emacs-using touch typists use right ALT all the time. ALT-x prompts you for a command, ALT-q in most modes runs fill-paragraph, ALT-f moves the cursor forward by one word, etc.
