1 - Reading the definition of simple assault in New Jersey - it appears as though he did break the law.
2 - In 2013 on film? To this point it is unique to him. Also - Bobby Knight won at IU, he has not won at RU. I haven't read any account of any player saying that their coach kicked them. Also - why is this a persuasive argument to keep a coach? It isn't required to be as bad as the worst, you can expect your staff to behave better. Also - considering the Tyler Clemente situation, I would say that what he did, and what he said, was an aggravating circumstance at Rutgers. 
3- By what measurement? Once the tape was released, I would say retaining him would have hurt recruiting. Also - the school is facing a whistle blower lawsuit from Murdock, which they will likely either settle to avoid the trial. Even if they go to trial - the coverage will bring this story back up/would have had the tapes released to the court.

I don't think it remotely compares to Sandusky, but that seems like an extreme metric to use as an expected guideline for coaches. The AD should have fired him 2 months ago. I'm not sure why he thought that those tapes wouldnt leak - as everything leaks, and that they had to figure Murdock was going to seek damages in court. I'm not sure why the decided to not fire him then. The difference now is that there seemed to be bipartisan support for him to go, and Rutgers is a state school. Firing him now would have come from further up the food chain than the AD, assuming he didn't make the call this past week.