Any facts behind that 20% claim? Have you compared Snap-On with Gearwrench? 1% is a lot to me.
I understand people buying Snap-On, because they can sell them later if they don't need them. Buying other off brands (be it SK, Proto...), the demand is far less. Those are way over priced and their quality is about the same or less than Gearwrench. Donating to the US workers in a dying industry that cannot compete is not exactly noble or patriotic.
The 20% is a subjective number I put to it. Not an objectively measurable.
I have compared Snap-on to Gearwrench; I have owned both. If I was just going to put a subjective to them, Snap-on would rate excellent, Gearwrench as "acceptable for the lower cost". Someone else might rate Gearwrench as great, and Snap-on as "not worth the much higher cost".
What I know is that there is a detectable fit difference between Gearwrench and the better brands. Not on every piece, and more so on some than others. But, overall, the fit is better. There is a finish consistency difference. Again, it varies, but overall it is better on the higher end brands. What is most subjective and hard to measure is the failure rate. I have seen a much lower failure rate (roundoff, not able to do the job, breakage) in the better brands. This mostly at extreme end of conditions, so again, each persons experience will vary based on what conditions they work under.
What you might see as 1% better might be what I rate as 20% better, or someone else might rate as twice as good. It is definitely subjective, and if you objectively measure only one thing (like tolerance on a particular bolt head, or hardness of the steel, or bending strength), you might miss the overall suitability. I guess that's why we argue about it on the GJ, if we could measure it, we would and everyone would just buy the "best". Or go down the list in order until they buy the "best" they could afford.