Usually salutations don't take up enough space to make a huge difference in the preview lines and taglines take up none at all unless the question is really short.
So, if the post has nothing else wrong with it and is just bookended with "Hi/Thanks", then you can probably pass on the edit. There are posts which need attention much more than these.
Also, cutting other filler-ish lines and rearranging sentences to make the edit seem larger so you can justify taking out salutations/taglines seems a bit childish. I've seen it in a few cases and would not like it to become the norm.
I think it boils down to the semi-personal nature of the site itself. It's half technical paper and half discussion. We aren't robots and we aren't speaking to robots. Some people just want acknowledgment of that fact.