The URL namespace is like being able to type ABCD into your browsers URL without http://www and the following.com and have it resolve to say www.yahoo.com.
There's no need to type http:// in your browsers address box. Your browser will add that. And, for a .com website, the www and the .com do not need to be typed. For example, to go to Yahoo!'s website, just type yahoo and hit Ctrl/Enter. Your browser will supply the www and the .com. And, the next time you go to Yahoo!'s website, just typing y in your browser's address box will bring up
www.yahoo.com unless you've cleared your browser cache and if you have not visited other sites that start with y. If you have visited other sites that start with y, then you may need to type one or two more letters, i.e. a, maybe h, and so forth, depending on the degree of similarity of the other addresses starting with y.
Right now, if I just type f, facebook.com/ appears in the address box and I can just hit Enter to go to the website. I'm using Opera at the moment but Firefox does the same.
You can also the Speed Dial feature with Opera or Firefox. With you can also enable the Bookmarks Toolbar in Firefox or the Bookmarks Bar in Opera to display most frequently visited sites on a toolbar at the top of the browser. So, I don't see the need for the "namespace" idea.