I think grandparent's point was that the part after the domain serves simply as identification of the information that is requested from the domain. Just like the foo in foo@bar.com identifies the user at that email domain. The user doesn't need to understand the particular implementation of the identification, just the principle "same string, same page". This is important to understand that URLs can be copied and used as links on the web. I've seen people not understand this: e.g. someone uploading a video to Youtube, then when I suggest to add a link to another video, or their Facebook page, not knowing that this can be achieved by copying the URL of the relevant pages out of the address bar. This is the missing internet literacy, and it seems unlikely that moving away from the "URL is just a piece of text" principle would make the understanding easier.
Sadly the simple principle of "same URL, same information" breaks down somewhat because of cookies (and, to a lesser extent, IP localization and user agent). http://facebook.com/ shows completely different information dependent on the logged-in account, and in fact that same person mentioned above was aware that URLs without a path part is the home page of that domain, and was thus expecting that http://facebook.com/ would show the same information to everyone. I'm not sure whether he/she really believed that the whole world should be seeing his/her posts, but it surely is a bad move by Facebook, it actively breaks the premise of URLs and is thus arguably damaging for internet literacy (and perhaps they are purposely doing it to mislead some people into a false sense of personal importance).
I agree with the first point, but it breaks down for me when you suggest that the principle of "internet literacy" is more important than making things easier to use for the user. I would not want the people building my car to have never invented the automatic gear, because they decided somehow that it removes me from understanding how a car works.
The difference is that understanding what a gear is is not essential to the functioning of a car at all. You can completely remove it without loss for that particular user nor for the community of car users.
Whereas not knowing that a URL is a piece of text which specifies a particular content on a domain and can thus be copied and used for linking is a loss both for the user and for the community.
You'll have to reinvent the principle of linking in another form to avoid the loss (e.g. every web and local app would need special GUI functionality to use instead, and the need for specification what to link would not be completely removable, unlike the gear).
Sadly the simple principle of "same URL, same information" breaks down somewhat because of cookies (and, to a lesser extent, IP localization and user agent). http://facebook.com/ shows completely different information dependent on the logged-in account, and in fact that same person mentioned above was aware that URLs without a path part is the home page of that domain, and was thus expecting that http://facebook.com/ would show the same information to everyone. I'm not sure whether he/she really believed that the whole world should be seeing his/her posts, but it surely is a bad move by Facebook, it actively breaks the premise of URLs and is thus arguably damaging for internet literacy (and perhaps they are purposely doing it to mislead some people into a false sense of personal importance).