I just like to add something that I myself was curious about: when you edit your post, the last post time will be updated to the last time you edited a post. So, editing a post essentially has the same effect as posting another comment, so don't worry about edits not getting noticed.
One more note: personally I believe it's a good thing to clearly mark edits. Something like 'EDIT:' in front of it should do.
EDIT: As for double posting, it's merely a definition issue. Your definition differs from ours, but what matters is that in this community, posting twice in a row is frowned upon, same content or not.