To me this is a no-brainer. I often have typos or formatting glitches in my posts and comments. Even beyond that I often rethink things after making a post, and it's often much better to do updates in place. Sure, there can be situations where the post changes enough that comments don't apply, such as the classic one where I initially post something uncontroersial like "I think genocide is bad" and then after everybody agrees I change it to "I heart Godwin's Law" behind their back. But as long as the "last edited" date is there, people can figure it out -- and bad actors will quickly lose credibility.
Ah well. They've reopened the discussion on Get Satisfaction, so we'll see what happens. It certainly doesn't seem like a smart thing to do when they're trying to raise funding from the community.