I got an interesting response here. I still don't get the logic behind it, but apparently, this draconian measure is necessary to combat certain irregularities experienced by those who maintain this website. By the way, you're able to edit your posts when you have up to 5 cows.
I think you mean over five cows. That may of course change in future.
We restricted editing because of the annoyance caused by people “correcting” their posts after they had been replied to, making the reply appear to refer to a non‑existent mistake.