Onto the explanation: this is not an issue. The ball detent is not supposed to be centered in the "V". It is in fact supposed to be hitting on one side of the "V" in order to keep the yoke tight to the frame. This is how the detent works.
I just picked up my 69 and found the same thing, had the same reaction, and received the same answer from the company. (When the call ended, I hadn't hung up for a few seconds as my hands were full, and I could hear her let out a big sigh on the other end.)
The written explanation is much better and, IMO, makes sense. I'm not a mechanical engineer, but I do have a high degree of mechanical aptitude and the explanation seems legit.
If the ball centered in the notch, the pressure would be equal on both sides of the notch which would basically be doing nothing but keeping that ball centered... if the crane were not fully seated for any reason the detent lockup won't care as all it's doing at that point is keeping the ball centered. With the ball putting pressure on the outside edge of the notch, it is putting constant pressure against the crane, keeping it closed.
I think what we are all thinking of initially is a detent designed to seat centered to hold a turning object firmly in a precise position. (like a scope adjustment knob) In this case the detent is designed to put constant closing pressure on the crane, which it would not do as well were it seated in the center.
Whew!
-Doc
EDIT: Even after writing that, another look at the alignment still makes me wonder. I'm going to go to the shops around here today and look at the 66's they have in stock for the same thing. (and any other models that use the method) I'll report back.
EDIT: I called two shops near me, explained what I was curious about, and asked if they wouldn't mind looking at theirs. This is what I've gotten so far:
66 - Centered
69 - Not centered
Governor - Centered
Governor - Centered
69 - Not centered
So, logic dictates that if S&W Engineering is claiming that it's by design for all models that use the detent, then the other models must be defective; they can't have it both ways.
I'm going to call and say that I have a 69 with a centered ball and that I would like to have it repaired due to reading on forums that S&W says it's not supposed to be.
EDIT: I guess I'm convinced enough at this point to not worry about it. I spoke with a different S&W rep who says he's been with them for 37 years, and he also said that it's by design for the purpose of keeping constant closing pressure on the crane. He said that the ones that look centered should still be slightly more to the outside than actually being perfectly centered. With the tolerances in design and manufacture, I can see how some models may be a little more down the notch than others, but the result is the same, if not more aesthetically pleasing. Despite costing the same, they aren't Swiss watches. So I'm going to go with everything I've heard that supports the not-actually-perfectly-centered design idea because it makes more sense from a mechanical standpoint than being centered. Centered just means it's centered; it doesn't mean that the crane is fully closed. Offset is constantly holding the crane closed. Case closed for me. Happy shooting!
-Doc