I don't really understand how you can group all of a companies products into one level of quality. Different models of lights from the same company will have different tube thicknesses, different heads, and possibly different switches. Therefore, you would have to look at the lights one model at a time. Of course, companies with bad quality control will sell lower quality products, but most of the manufacturers you listed have good QC.
What is the definition of a "high quality" light? People always talk about the "quality of the machining," but what does that really mean? I can understand that threads need to be machined precisely, but why should the outside of the light really matter? I suppose knurling could be an issue, but I don't see how the quality of the knurling would be relevant; it is the style/type of knurling that determines how good of a grip you have.
As far as durability goes, most of the lights sold by these companies are aluminum, so they will not break if you dropped them. Incandescent bulbs, on the other hand, can break if you drop the light, so would the surefire incan models not be considered durable? An important quality issue would be the switch, but I have seen no empirical data that suggests that any brand's clicky switch is any less likely to fail than any other brand's. I would think that any premature failure would be from some small defect in manufacturing, but I believe that you probably have an equal chance of getting a bad switch from any of these manufacturers.
These are flashlights, not finely tuned machines. They don't have many moving parts. Therefore, I don't really see what effect "build quality" really has on the reliability of the light, or even how quality can be objectively measured.
Wear on the outside of a light should have no bearing on the operations of a light, so I don't see how the quality of the finish is really relevant to durability either. Therefore, I think that good customer service is probably more important than purported "build quality," since you can get a bad light from any manufacturer.
Of course, some of the cheap chinese lights (from DX/KD) will not have the same quality (no matter how you measure it) as any of the brands listed above, since they probably have minimal quality control, and price their products very low (which may mean that they use inferior parts). They also tend to not look as good visually (although this shouldn't affect durability). However, I wouldn't expect something like this from any of the companies that the OP listed.
