Why do the URLs of posts here change?

[Rustom Mody]

On Friday, January 9, 2015 at 10:27:53 PM UTC+5:30, Chris Angelico wrote:
> On Sat, Jan 10, 2015 at 3:52 AM, Rustom Mody wrote:
> > Is it?
> > Ok lets test that.
> > This is posted from google-groups.
> > After posting I shall remove it
> 
> Remove it from GG, maybe, but I doubt very much it'll be removed from
> the python.org archive. It's virtually impossible to remove something
> from everywhere... you have to find every copy and hope none have been
> web-archived yet.
> 
> ChrisA

Precisely my point.
Removing something from the web is really a meaningless activity
[apart from some moral feel-good factor]
If that gesture means something to you, GG provides it

And to the best of my knowledge it does not screw up links like mailman.
We can test in some limited way that but I dont know how to do any test which will be
reasonably exhaustive