This is an idea you could immediately throw at the bottom of the list of ideas for improving the site (and keep there for a while). It's been on my chest for a long time, and I just wanted to get it off.

Instead of edited posts being noted as edited only if the edit has happened after a certain amount of time, maybe it could be beneficial if the noted post is noted so only in the event that someone has read the post in the time since the post had been edited.