In addition to what initall mentioned, having a standard for user directories would allow for URL pattern matching such as, "anything that starts with tilde, treat the remainder as a user's name, and see if they have a website". While I don't know if this is how any universities handle their serving of users' websites, it would be an option. If a user existed with the name "employment", but they wanted to setup university.edu/employment to load employment information, the tilde helps avoid conflicts.
(Obviously, if they're using a subdomain like
users.university.edu/<username>, this isn't needed. Additionally, they could also use a more user-friendly URL like
university.edu/users/<username>, but the tilde being preferred for reasons initall stated).