I strongly agree with both tomcatt51 and gunblade. Some folks have learned DA shooting well enough that retaining a SA capability is not a significant advantage. I feel that way, and would prefer not to leave a SA notch on a bobbed-hammer revolver so that someone else can screw up. However, at present, my revolvers are only for me, and I honestly can not tell you for sure which few of my bobbed-hammer revolvers have a single-action notch, because I don't actually care. I already know that I will not use them that way.
The original reason for removing the notch, AFAIK, was to avoid bogus charges like those levelled against a policeman who righteously shot a perp in a video arcade in Miami, I believe in 1985. He was wrongfully accused of having cocked his revolver and then accidentally discharging it, when, in fact, he intentionally shot the perp in necessary defense of his own life. After that, many PDs went DAO so that there was simple physical proof against such bogus charges.