I think Larry has it. The hammer was changed for ease of conversion from rimfire to centerfire. If I remember right, back in the day, a few of the "expert" gun writers complained that the screw design forced them to carry an extra screw driver in the field. Or, if you swapped the barrel from rimfire to centerfire (or vice versa) at home and forgot to rotate the hammer screw, you were hosed in the field. My feeling is that if it 'aint broke, don't fix it. There are no safety issues with the old style hammer that caused a "redesign" that I'm aware of.
It would be different if you were having problems with it, or the hammer was broken, etc. As "dry firing" was mentioned, my opinion is that it's not really a good idea to dry fire one anyway. If you MUST dry fire one, you can by just opening and closing the frame, then just pull the trigger without cocking the hammer. That will give you the feel of the trigger release, if you're trying to "learn" your trigger.