Pin Play
There are several Hammermounted firing pins that don't have any play. My Naget revolver has a long riged firing pin, along with my rimfire pistols, and it gives me the willies. I can see how having a little play in the pin would help guide the pin in the opening. I also wonder if the it is a repair issue. On my old Smith 19, if the pin broke, I wouldn't have to replace the entire hammer.
Good question, I always wondered about it myself.