Coming from a technical background, this sounds crazy to me.
For instance, we are looking to migrate to Confluence for our documentation needs but it is unclear where everything will reside in the Confluence structure or what titles the pages will have. This human readable "feature" breaks bookmarks, links and emails during the movement period.
It is crazy that renaming the content page would break someone with a bookmark.
Since there is a already fallback case for the l18n standard and uncodable characters such as punctuation, it wouldn't be that difficult to provide administrators (like myself) with the power to switch to the ?pageId=XXXX thus providing the stability for users to change the names and move content around as they see fit.
Human readable page ID (slug) is important feature that drastically simplify maintenance of complicated multi-space project. It's easier to maintain consistency of links like .../PROJECT/Release+Info than ../pages/viewpage.action?pageId=341003791
But I find very confusing, that confluence auto-generate this human-readable slug from the page title and it's not possible to update slug manually or change page title later without breaking links. I.e. I would like to have a page .../PROJECT/Risks+Issues with the title Risks and Issues.