No insult intended. Just a differences of opinion.
I think some people just like seeing the hammer move. Based on comments I've come across on other forums, it's as if it kind of lets them "see" their trigger press and perhaps why they believe the action is better on a gun with an exposed hammer vs an internal one.
As to why the Centennials may actually have better actions, it was in the article I shared...
"
Grant Cunningham, master wheelgun-smith and author of the excellent Gun Digest Book of the Revolver, writes the following at his blog at Personal security training and advice - [url]www.GrantCunningham.com www.GrantCunningham.com[/url] "… the Centennial models simply have better actions! The enclosed hammer Centennial models have slightly different sear geometry than do the exposed hammer models, which gives them a pull that is more even—more linear—than the models with hammer spurs. For the savvy shooter it's a noticeable difference, making the Centennial a bit easier to shoot well."
Grant continues, "The Centennials also have one less part than the other models: since they have no exposed hammer, they don't have (nor do they need) the hammer-block safety common to all other 'J' frames. That part, which is quite long and rides in a close-fitting slot machined into the sideplate, is difficult to make perfectly smooth. Even in the best-case scenario, it will always add just a bit of friction to the action. Not having the part to begin with gives the Centennial a 'leg up' in action feel. (In fact, at one point in time a common part of an 'action job' was to remove this safety, in the same way that some 'gunsmiths' would remove the firing-pin block on a Colt Series 80 auto pistol. Today we know better!) So, if your criterion is action quality, the choice is clear: the enclosed hammer Centennial series is your best bet!"
And in terms of single-action capability, Ayoob mentioned it in the article as well. I would add extreme close-quarter and contact distance functionality to the reasons why an enclosed hammer makes more sense. Michael de Bethencourt and Grant Cunningham also advocate that defensive revolvers should be DAO since single action capability presents more overall problems than it does benefit, especially with pocket snub-nosed revolvers. There's plenty of articles out there going over the issue in detail. There may very well be some instructors who recommend it, but none that I'm aware of or follow and I think there are very valid reasons why that's the case. It's obviously yours or anyone else's prerogative to disagree.
I think mine was the only negative review (other than recoil-related) and it was only because I bought it on-line instead of locally. Had I found it in a local shop I would have quickly detected that something was wrong with it and possibly gone with a different one instead. 
