Preventing bench-clearing brawls: A comparative analysis

So Kyle Farnsworth didn't get tossed for throwing behind Manny Ramirez's neck following Ramirez's two home runs in tonight's Red Sox-Yankees game. When the two teams meet again in July, someone will almost certainly retaliate, and a fight may well break out. Which raises a (semi-)interesting question: what's with the totally distinct prevailing approaches to punishing bench-clearing brawls in baseball, basketball, and hockey?

In the NBA, if you come off the bench to join a fight, you're definitely getting suspended. In the NHL, you can pretty much pound someone into paralysis if you're on the ice, but it's more or less frowned upon to come off the bench to do it (regardless of whether you're going onto the playing surface or, um, into the crowd--see supra Terry O'Reilly in his playing days).

In baseball, though, dugouts and bullpens emptying is essentially a rite of summer. And no one gets suspended for coming onto the field specifically to fight unless things get, like, really out of hand.

Resolved: it is because we are racist/anti-Canadian that we fear bench-clearing brawls in basketball and hockey, but not baseball. Discuss.