Considering a subdomain "trivial" is ridiculous... there's a difference between "www.example.com" and "example.com". Not only can they serve different sites, they can even have different DNS records! It seems that "m." is also considered a trivial subdomain. So when a user clicks a link to a "m.facebook.com" uri, they'll be confused why FB looks different when the browser reports it's on "facebook.com". I sincerely h…
>there's a difference between "www.example.com" and "example.com" Can you link to a site where these two are different?
For example, with Active Directory, the DNS A record for your foo.com domain must resolve to your domain controllers. Your www.foo.com will resolve to a separate non-domain controller web server.
I think a lot of the commenters here are thinking solely in terms of commercial web services such as twitter.com and such, but there's so much more to the wider landscape.