It's not a suspension he's worried about. In general it's not a good idea to show up the umpires or call them out after a game, you don't want guys who have a large part in deciding the outcome of ballgames holding a grudge against you.
It's easy as fans to wonder why Leyland didn't go into an expletive laden rant about how shitty the umpires and Fairchild in particular are, but in his position you have to look big picture.
It was a bullshit call, and Leyland could be seen on TV yelling "BULLSHIT, BULLSHIT, BULLSHIT" at the umpires, but we don't want it carrying over into the next series.
And while we (as fans) might all love to see an "oops" type crossup and see Fairchild drilled, it would never happen, because that's bush-league shit and the Tigers are better than that.