Scott, good point and I don't mind adding that but from what I've seen over the past several years is that people can learn to shoot just about any gun. It seems to be more of a training issue rather than a hardware issue. For example, a 1911 seems to be comfortable in anyone's hand including mine, but it doesn't meet other criteria which are more important to me.
You've been training people for many years though, so please define what a correct fit is.
When taken in the context of this, or any other gun forum, the need for a perfect fit is arguable. When put forth to the general public with less enthusiasm and experience it can be paramount to their success.
The mechanics of shooting are going to be different for every shooter because every shooter will be shaped somewhat differently. Fit to the hand is important. That fit is generally defined by asking the shooter to let their strong hand hang naturally at their side and then having them make a loose horseshoe shape using their thumb and fore-finger. This is horseshoe shaped slot is where the gun should fit. Generally it will create a base form which to begin. Once the pistol is placed in the hand while at a natural hang to the side, the student can then take a natural grip of the pistol. Bringing it up to a natural point and the gun should point well because it is aligned with the radius and the ulna. It should feel natural and the shooter may even want to point with a slight interior cant of the hand. At this point is where fit becomes more difficult.
The shooter may not be able to reach the trigger or other controls of the pistol using this natural grip. Because of this certain accommodations must be made. Those come in the form of a different gun, adjustable back-straps, grip panel changes and trigger length adjustments. These points of adjustability must be adapted, along with type of gun chosen, until the shooter can find the adapted fit that is closest to their natural point fit. Sometimes there is no need to adapt at all.
Some adaptations are more difficult than others. Hand size, finger length, palm length, overall girth and width of the hand are the primary considerations, but shooter strength and ability to follow simple instructions are just as important. While I agree that nearly any healthy person, when using proper technique, can operate a handgun, there are many out there that feel they can't. So it is important to understand that it's not what I think, it's what they think. I can demonstrate and teach the proper techniques for cycling the action on a handgun, but if the student doesn't believe they can do it, alternatives must be found until they gain the necessary confidence to do otherwise.
In this case, we stretch the term "fit" by including the operator's ability to satisfactorily perform the basic manual of arms for their chosen (or chosen for them) pistol. For example, a woman comes to class with her husband and he, with the advice of the gun store experts, bought her a LC9. Now that is normally a good gun, but is it a newbs gun? It fits her hand and is small so she can carry it pretty easily. This is where the ability to operate the weapon comes into the fit category. The lady can't operate the slide easily and, with the help of her husband, is embarrassed. She has a difficult time operating the gun because the 115gr ball barks a lot in the micro 9mm guns and the only other time she has fired it was when he husband decided she should use the SD ammunition he had on hand so she could get the "real feel" of the gun. Ultimately, she has a gun that doesn't fit her properly and she is having a series of nothing but horrendous experiences with "her" handgun. Nothing good can, or will come of this mess. Fit is important.
Fit is so important that S&W, Glock, Springfield, HK, SIG and FN all offer some type of an adjustable grip and/or trigger system for their guns. The reason the HK P30 is so valued by knowledgeable end users is because it permits complete interchangeability of the back-strap and both side panels. That is how important fit is to the smaller hands of the european users. The 1911 fits because it is a single stack and most single stack guns fit better. If you doubt this, grab ahold of a P239 next to a P229 and you will see what I mean.
Fit matters to the high end users and the newbies alike. What is posted on this site is reaching far beyond the average gun-person's realm. People seeking information come on here and read a few comments and walk away with what they believe to be a correct answer. A simple list, such as the one you have created is very helpful for them. Because of this we, collectively, have an obligation to ensure what we say is not only accurate, but complete. We reach beyond ourselves and we need to recognize that when we say things like
I don't put any faith in the gun that fits.
It seems to be more of a training issue rather than a hardware issue,
that they are not necessarily correct. While either may or may not be true, they send a very broad message which lacks context or support. They are rightfully stated opinions of those people who made them, but they are not necessarily based or supported in a breadth or depth of fact, data or empirical information.
I have trained thousands of students in my days. I have worked with everything from the super-ninja to the average Jane. What I have learned in working with these people is that fit matters. The ability of the operator to operate the controls of the gun properly, matters. The time it takes to train a student falls off exponentially when they have a gun that fits them correctly. Most important of all, the shooter holding a gun which fits them correctly is a more confident shooter and sometimes confidence is all they will need.