I do remember asking this same thing. I have absolutley no idea why , but and I was told that some do and some don't .
I remember asking cause when I installed the race hammer in mine ( with notch ) I filed it down, as it could be dropped from half cock by pulling the trigger , which I did not like at all. It prob does not have enough momentum to set a primer off , but I did not want the confusion of a dropping hammer.
I probably needed to do some other modifiction to rectify this , but I remember I could not figure out any other way than file it down, and when I read that some do not have it I kind of relaxed a bit.
Mine is a 75B so it comes with a firing pin block . Since I had modded the gun myself I did not want to risk any accidents so I left the FPB in there. The gun worked flawlessly for hundreds of rounds so I am quite confident in it. But the FPB stayed. I bought all extra parts, so I can revert back to original state any time. It is a fun gun for the range , so I'm not too worried .