Plenty of people post things that they shouldn't have and regret. It could be plainly incriminating, like when people ill-advisedly make a post essentially admitting to a crime, threatening someone, or discussing events related to a lawsuit in public. It's possible deleting or obscuring such a post could even be construed to be destruction of evidence.
Point being, the ability to edit and view edit history changes very little with regard to the courts. Instead of needing to present Facebook with a subpoena for information from e.g. logs, you're able to simply view history. It doesn't change anything whether you can delete the data or "delete" the data, it just changes how accessible it is.
http://www.wassom.com/delete-at-your-own-risk-spoliation-of-...
As far as the rest of your post, i believe that is exactly what I was asserting originally.