[TwelveNights]

I've always thought that Twitter adopted the same line of thinking, preventing tweets from being editable.

[jedberg]

I think it twitter's case it was architectural. By treating tweets as immutable the could publish them on a pipeline and not worry about duplicate copies around the system being out of sync.

[mattnewton]

That and early on it used sms as one of the interfaces, which is not editable.

[fortran77]

It's to prevent tweeting "LIKE this if you like Ice Cream" and then editing it to say "LIKE this if you like pedophilia"

Nobody would ever Like/Retweet anything if it could be changed later.