DAVID BYRDEN
I will explain the need for URLs with a simple example.
If you're looking for a person within their family home, you can call their first name and expect a reply.
But in a public place, where people from many families mix, there could be several people with that name. To resolve this ambiguity, Western society gives each family its own "surname".
In XML documents, data from different namespaces is often mixed. Therefore we need surnames of some kind,to identify the namespaces themselves. And these should be globally unique; we don't want to add third and fourth names later.
So, the inventors of XML needed a system of globally unique names. Such a system already existed and was widely known; the URI system. (We all use URLs, which are a form of URI.) The XML experts gladly adopted this system, saving themselves some work!
So, each XML namespace is given a unique URL. The URL is its name; it's not an address. You can put the URL in a browser address bar if you like, but nobody guarantees that you'll find anything at that address.