I guess I can paraphrase my question as this:
Are there some arrests that will lead to charges being filed (ie: maybe the charge was not filed immediately due to processing speed - like the Crown isn't present at the time of the arrest but it's a slam dunk case and it is reasonable to assume that once the Crown gets to it then charges will be filed) and some arrests that may lead to charges being filed?
You are assuming that arrests only may lead to charges being filed, and your subsequent points are based off of this fact. I don't want to make that assumption. So my question is that is it possible that MR knew that he would be charged in due time and does the arbitrator take this into account?
Additional examples that muddle things regarding whether arrest alone is sufficient grounds for termination:
http://www.eeoc.gov/laws/guidance/arrest_conviction.cfm#VB2
An arrest like disorderly conduct (being rude to a police officer) is not grounds for termination.
An arrest and dismissal of charge can still lead to grounds for termination. The defendant argued that he wasn't charged and only arrested (innocent until proven guilty was used) but the commission agreed with the employer that the facts brought forth by the arrest was sufficient reason to uphold the termination of that employee given the argument that the employee's argument (it was based on discrimination).