I've been reading The Absolute Sound since the very beginning, and read Stereophile from the very early days, when J. Gordon published from Elwyn, Pa. Neither publication at the time accepted advertising precisely because they claimed that they did not want to be influenced by those dollars. (I'm not sure that accepting advertising compromises editorial integrity, but both magazines eventually gave way- I think HP was still at the helm of TAS when that happened, I don't remember when Stereophile started accepting ads, but it doesn't matter if there is a separation between the editorial and the advertising/marketing at the magazine. I gather most people think that this separation is impossible).
What I do remember from those early years is that there was far less "high end equipment" and the reviews could be critical of certain aspects of performance without altogether panning a piece of gear. As I recall, there were few bench measurements in either magazine. I still have my boxes of old TAS issues, my collection of old Stereophiles is spotty but it might be worth going back to re-read some of them. I'm willing to bet that the reviews probably weren't much more 'in depth' than a lot of reviews today- I think there was less skepticism, perhaps because the industry was less mature, the practices of quid pro quo weren't as slick and maybe we had more faith in the integrity of the reviewers. (or perhaps I'm simply naive). The high end industry is typically small companies; granted, there has been consolidation, ala Harman, but compared to other consumer product manufacturers, a company like Wilson or Magico is not a huge company.
By comparison, somehow automotive magazines manage (at least some of them) to do pretty thorough reviews and tests of performance cars. They may not do completely negative reviews, but they often do comparisons which will be pretty plainspoken, not only about measurable specs, but handling, driving experience, tactile aspects, reviewer preferences, etc. Unless it is simply the size of the ad budget of Porsche compared to Wilson, or the size of the readership, I'm not sure why car magazines can successfully pull this off and audio magazines cannot.