...And why would anyone purposely do that, given the option of a manual safety? That'd be a little like carryin' a cocked revolver. Doesn't make sense.
What I said was, Browning originally designed the 1911 to be carried that way. The original design did not have a thumb safety. The Army asked for it to be added later. Don't make the mistake I am advocating carrying a 1911 this way, for I am not.
While Browning did design weapons per customer request, he also designed many on his own initiative. Browning was not the only one to submit a handgun to the Army for consideration. His design had to beat out the others, so he did have to sell his design to his customer.
The half cock notch is to catch the hammer in case it slips while being thumb cocked, same as the half cock of the Colt SAA. It may have been originally added so the shooter had the option of carrying the 1911 safely the hammer down on a loaded chamber, but the half cock sear isn't enough to hold the hammer if it takes a hard blow such as if the pistol were dropped and landed on the hammer