We've been working on this for some time and will implement it in the future. It's never been one of our top priorities but we agree with you that it would be nice.
Why it's never been a top priority is that in many forums which allow this function, you get someone who comes in and makes a post and causes some trouble or instigates a situation wherein a bunch of people respond -- and then the originator edits or removes their original post making the thread look rather nonsensical because the thing that started it all is now gone.
So we have been developing the edit function to allow edits but only for 10 minutes or until someone posts a responce, which then locks it.
Thanks for your feedback and for being a part of the Cow.