I'm on board with this. Seems reasonable that OP can delete the OP up until someone replies but not after.
Just before posting this, I saw that Steven disabled deletion.
Still, here's what I had already composed as a reply and my opinion:
Ideally, I think there should be a grace period of say some 15 minutes where anybody can decide to remove his post completely.
It's quite human to write and post something in the spur of the moment, and then regret it shortly after(*).
But after that, and especially when another member answered, it should be in the hands of a moderator.
But, SMF is probably very restricted in what can be set in this repect.
Let's await what AvikB can tell us about this.
(*)
This isn't the case for the new member's post and deletion today.
After some unpleaseant PM's he has the doubtful honour to be the first and only forum member in my eight years presence on this forum that I had to block from receiving any more PM's.
So, since education and good manners seem to have failed for some, perhaps technology can help us out a bit here ;-)