> Are you referring to the brief period in which a handful of tech companies colluded to tamp down salaries and cross-recruiting?
Ignoring for the moment I don't think four years is very "brief" or eight is only a "handful"[1] (and it may actually be even more[2])
It's a bit naive to think this "had no significant impact on the national average salaries" - some of these companies are/were among the largest and most desirable companies in tech, what they do is going to affect the entire industry.
e.g. if you are a hiring manager at a company not involved and are trying to hire someone who is also considering an offer from an involved company the amount you need to offer to be more attractive is less. This brings down the average you pay, which brings down the average you offer. Likewise companies now competing for candidates also receiving offers from you now have an easier time sweetening their offers, and so forth and so on.
What is naive is to assume without evidence that the actions of a handful of companies that employ a tiny percentage of software developers had a significant impact on average salaries nationwide. In the absence of any such evidence, it makes more sense to assume it had little impact, which is what I do. The example you cite is mere speculation, and one could easily speculate about an opposite effect, i.e., companies that would not ordinarily be able to compete with Google et al could offer candidates more than they otherwise would have, that is, they might be inclined to stretch salary offers for star developers rather than shrink them. But, there's no evidence that either thing happened to any significant extent.
The example is hypothetical, but it is not speculation. A candidate [usually] decides to accept an offer or not on a number of factors. As a hiring manager you are unable to change most of these factors (e.g. you cannot change the tech stack, or the company culture, or the location). What you can change (to make your offer more appealing than others a candidate is considering) is the pay.
If you're considering another offer for X, I can make my offer more attractive by exceeding X. The lower X is the less it cost me to exceed it. If some companies (particularly large and desirable ones) are lowering X that will affect far more than "just" the 64,000 members of the class action.
Ignoring for the moment I don't think four years is very "brief" or eight is only a "handful"[1] (and it may actually be even more[2])
It's a bit naive to think this "had no significant impact on the national average salaries" - some of these companies are/were among the largest and most desirable companies in tech, what they do is going to affect the entire industry.
e.g. if you are a hiring manager at a company not involved and are trying to hire someone who is also considering an offer from an involved company the amount you need to offer to be more attractive is less. This brings down the average you pay, which brings down the average you offer. Likewise companies now competing for candidates also receiving offers from you now have an easier time sweetening their offers, and so forth and so on.
[1] https://en.wikipedia.org/wiki/High-Tech_Employee_Antitrust_L...
[2] http://pando.com/2014/03/22/revealed-apple-and-googles-wage-...