[kentaromiura]

IIRC on windows 3.1 keyboard navigation X was always the key for exiting, as E was already used for other things.

I clearly remember that for closing windows one could do alt+f4 (which was itself a shortcut to Close) or open the file menu (Alt+F) and select eXit.

I can't check but I believe it was the same for Write and notepad as well and any other programs that had the Exit option.

So maybe that's where the windows 95 developer took inspiration for the X icon