URLs can and do change, and as long the change is performed gracefully, nothing is lost. The content is the thing, and the convenience of the user has to be the goal in mind.
Perhaps it’s time to acknowledge that the web’s infrastructural user experience should emphasise the humans who are doing the browsing, rather than the machines serving up the content.
I’d be okay with pushing URLs a bit more behind-the-scenes. After all, as Matt points out, how many of us routinely navigate to a website via its URL? Typing them is a pain, remembering them is a bigger pain; these days, they’re purely a routing and navigation system. The navigation system most people use is a search engine, or a personalized bookmarking system.
Relatedly, I’ve had similar thoughts on telephone numbers lately.