I agree with most of what has already been said. For Art 2 it's just a business. He's content as long as he's making money. Winning championships would be a nice bonus but not the ultimate goal. He's no better than Mike Brown.
And I do think there is something in his ego about maintaining stability and doing things "the Steeler way." Again, that's more important than winning. The appearance of stability and being in control, not making rash decisions or having knee jerk reactions when things go bad.
I don't know if this is true but I've heard that while Tomlin's pay is in line with other head coaches, the assistants are paid below league average AND more importantly the Steelers' coaching staff is among the league's smallest (fewest assistants). I can't imagine that is Mike T's decision.
Finally, I don't think Mike T's race or the Rooney rule should have any bearing on whether he's retained or let go. The results should matter. The team hasn't won a playoff game in years and hasn't been to a Super Bowl since 2010. Hovering around .500 and barely making or missing the playoffs should not be considered success.
Mike T accomplished a lot and deserves all the accolades thrown his way. We can be fans of Mike T and appreciate him for what he's done while at the same time thinking it's time for him to move on. I think he's a great guy and had a great run as coach, but just like Noll... at some point we need fresh ideas and new blood.