Good point - but offset by the fact that three words become instantly more memorable than a random set of cruft generated by the likes of Lastpass. I would only use w3w to manually create the password, not to access (or store) it via any interface. The only benefit (cf inventing my own three words for a pasword) is that if I do forget it, I just have to have also remembered or documented the location to retrieve it - but as you say, only if they are still in business.
Maybe I’Il just tear off another post-it, instead, and add to the others on the frame of my monitor! 
