It was voted for by the staff, a while ago, David, and this was the outcome. I voted for the present idea, but, now, I realise, it does handicap the poster if he/she suddenly realises that some wrong info was given.
There is a problem, if users are continually allowed to update posts,
Ian will probably post something here, whatever the decision.
Here is a classic example. I have come back with a further thought. It is easy, and probably more significant and reliable, if the poster refers to the earlier post in another, with the update - just a thought.