I see no need for any such rule. There are such things as badge hunters. There are such things as minor editors. There is nothing we can do about this.
Now something to point out is that the second edit was made by a reviewer (guntbert) of the first edit.
Now he decided to approve the edit, but remove the bold and add a tag. A perfectly valid choice.
Now personally, a comma instead of a period looks weird next to numbers, but it isn't something I would edit for; and, when referring to something like a microphone, working fine makes more sense than doing fine. Again, nothing I would edit for.
Now you might have figured out by now; edits are subjective. Everyone has a different, perfectly valid, opinion. Like the FAQ statesFAQ states if you have a problem with people being able to edit your posts this probably isn't the place for you. Try the Ubuntu forums.
If someone changed something you were particularly partial to, just role the edit back and move on.
There is no need to complain, no need to argue. It's a big world ;-)
note: If another user starts an edit war, repeatably editing something you have rolled back, custom flag the post and a moderator will take a look.