True, most of the misses are due to the shooter and not the gun, but we arn't talking about misses. We are talking about the fine line between decent accuracy and outstanding accuracy.
For many years, I didn't buy into the whole modified or "custom" gun concept. I figured that all my guns shoot better than I do, so I really couldn't appreciate the difference these modificaitons make. That was until I shot my first truely "custom" gun. Since that time I have fired many "custom" guns and realize that it does in fact make almost any shooter, a better shooter. I once read an article in the Beeman airgun catalog about why you should use "good" air rifle pellets. The logic made a lot of sense to me. Basically it goes like this. Lets say you took your handgun and shot it in a machine rest to find out it's ultimate potential accuracy using that particular load. Then you actually fire that same load offhand to see how well you can shoot individually; how much error is introduced by the human factor. The groups you can shoot offhand are a combination of human error, added on to the potential accuracy of the gun. So let's say that the gun will shoot a 2" group from the machine rest and you can shoot a 5" group offhand. If you can cut the machine rest group to 1", this will also translate to an improvement to a 4" group offhand. Since your offhand accuracy is a product of both intrinsic accuracy plus the human error factor, you offhand accuracy can be improved by improving either one of the two factors. One is mechanical and one is human. The machanical can usually be readily improved by things like having a fitted match barrel (and good sights, and good triggers, good frame/slide fit, accurate ammunition.............. each one is a piece to the accuracy puzzle and all add up to improve the potential or actual accuracy of that particular gun). We are all constantly trying to improve the human factor.
Having a match barrel fitted is no big deal. I believe Bar-Sto charges $15.