Note the structure of the 'persistent url' used by Blogger:
It contains the year/month/date and text taken from the subject. In database terms, it is the date (YMD) and subject text that uniquely defines a posting. Change either and any links to the prior posting will break.
I would have much preferred a level of indirection with a unique ID for a blog posting. This design, if deliberate, says quite a bit about how the Blogger engineers think about blogs and blog postings. Heaven forbid one should have a typo in subject line! It can never be fixed, or the links to the posting will fail. Likewise, if one wishes to update a posting and draw attention to it, one must edit locally and not revise the date, then create a new posting pointing to it.
These are fundamental design decisions, but they will be invisible to most users. Much software is this way; the mechanics of identity (in this case blog identity -- foreign keys in other words) are the invisible 'deep themes' of the software.