Seriously. Look closely at the first pic posted by 500 Magnum Nut. in order to get a gun to go off, it needs to be dropped HARD... hard enough to snap off the part of the hammer with the single action sear (the whole part resting on the rebound slide)... and even then, chances are that the hammer won't move forward because the double action sear rests on the top of the trigger. This kind of "perfect storm" of events probably would only occur on a gun with some defective imperfections in just the wrong spots in the metal of the hammer, trigger, etc.
You know what else might happen? Maybe you get a piece of debris that finds its way between the hammer and the firing pin and the tap on the back of the hammer is enough to set the gun off even if the hammer block is in there. Is that likely? Hells no. Could it happen? Maybe. Maybe another piece of debris makes it behind the primer on a live round and there is enough endshake in your cylinder that a round gets set off if you drop the gun. Likely? No way. But I suppose it's *possible*.
As has been mentioned, back in ye-oldie-time days, the SAA would just have firing pins resting on live primers if you weren't careful. Because of this, the myth persists that modern revolvers have similar issues.
Would I stand in front of one while you dropped it from holster height onto its hammer over a loaded chamber? No. Would I bet a sizeable sum of money that it wouldn't go off? Most definitely.
Leave the block in there if you want. You'll probably never notice it other than a rattle in the gun at times. However, the SKY IS NOT FALLING. Sheesh.
And for God's sake... stop dropping your guns on their hammers. What's wrong with you!
