I'm sorry, I haven't explained my motivation well enough:
URLs are "machine text", not "human text".
Practical examples would be: Easier to spot phishing URLs, easier to mark and edit parts of the URLs.
In fixed-width font every character has the same width. Useful in coding mostly because succeeding lines are aligned precisely to each other. But, to get a little more philosophical, it also gives the message of: "Every character is equally important". For example, a dot is very important in code, and it has the same width as other characters in a fixed-width font. But in "human text" dots, while still important, have a tiny width.
In a URL a dot is very important, and thus shouldn't have a tiny width. It often happens to me that I want to select text before/after the dot in a URL but it's so hard to do it precisely because the dot is so small.