I assume it started as a kindness to 80 character wide terminals a lot of people use to browse HN since it was an easy way to pick a limit, the same way Twitter

I assume it started as a kindness to 80 character wide terminals a lot of people use to browse HN since it was an easy way to pick a limit, the same way Twitter's original limit was the length of an SMS and stayed that way long after apps became the main way to interact. Let's make it 140.