Not understanding URLs also affects their ability to see through any bad emails that make it through the spam filters. If you understand URLs, you can hover over a link, see that it's pointing to bankcom.fzzaa.net and see that it's obviously not something you should click on.
Quite a few students have asked me how to access the online resources that come with the revision guides they have purchased. Somewhere in the book will be a URL to whatever they need and they just don't recognise what a URL is. They see something beginngin with https:// and it's meaningless to them. Visit this link? How? What is it?
This isn't an exhaustive list of reasons, it's not even close. I don't think it makes sense to argue that being completely oblivious to the very basics of something so fundamental to all our lives is something to be dismissed as irrelevant. I also thinking it's bad that Google is the only way so many people know how to access a website. Remember when some blog was ranked #1 for 'facebook login' for a day or so? People were filling the comments section with stuff like "ugh this new facebook is so bad". I think that highlights a serious problem that we're lucky enough to have mostly avoided... so far.