RPK,
If you are not in or have never been associated with a large law enforcement organization, then you would not know why they were and probably still are needed. I saw at least 2 firearms instructors fire off guns in a "ACCIDENTAL DISCHARGE" situation and these were supposed to be the service experts with firearms. Accidents can happen.
Now remember that many of the people in law enforcement today have no military background or firearms background. They have exactly 1 gun and it is the one that was issued to them. They don't compete, they don't shoot on their day off or go hunting in the fall. They shoot when they qualify and that is it.
It is a major reason behind the move back to the 9m.m. from the much vaunted .40 S&W caliber. People were simply having to much trouble qualifying.
DAO is perfect for these people as there are no safety's to engage or disengage. You never have to lower the trigger on a cocked gun. You can never accidentally engage the safety when you are trying to draw and fire as quickly as possible. You will never leave the safety engaged unintentionally after dropping the hammer.
You have a longer, but not necessarily heavier trigger. I found that I could shoot a DAO pistol just like a double action revolver, but reload much quicker and only half as often.
If you doubt it, try a really good double action only like the BERETTA 92D or 96D. They are very easy to shoot well.
If you remember who the target audience is, then they make a lot more sense than just about any other type of pistol. I think they are safer than DA/SA or SAFE ACTION pistols like the GLOCK or the traditional 1911 style single action. I base this on my own experience and from observing other officers on the range.
Jim