Web pages move too
We don't always think about it, but web pages move too. Websites, databases and other information systems aren't static: they get built at a particular point in time, with particular expectations, on particular technology. In an ideal world a URL never changes — Cool URIs don't change, as the saying goes. In practice, something always changes: cool URIs don't change, real ones do. Deal with it. (For this post, feel free to read URI and URL as synonyms.)