> I think there is still some duty to a website creator to consider what else people might want to use it for.
I could not disagree more with this opinion. The creator presumably hosts this website on her own dime & invested the time and effort to create this piece of art - and you are connecting to their server, free of charge. I don't see how you could reasonably claim that they have a "duty" to do anything.
You're right that an image of a nude woman would be make this unacceptable in a school setting - however, it is your duty to vet the content that you show in class, not the other way around.
Finally, I don't see what educational purpose this would serve - as it's not like this is actually an OS, perhaps as an example of html5/js programming or nostalgia. In fact the whole thing is a JS app, so there is nothing stopping you from running it locally, where you can edit to your heart's content. Ironically the first JS file I clicked on (desktop.js) contains the shortcut definitions for the desktop.