The issue with VW diesels, if that is what you are referring to, was an attempt to run around the EPA (and CARB) schedule, which dictates whether automobiles can legally be sold in the US (and California, which has its own view of things). [
FWIW, the reason VW got in trouble wasn't because VW couldn't produce a 'clean diesel' engine. They just couldn't do it at their price point. The main issue was that the company didn't want the end user to use as much DEF additive, which gets expensive. DEF is required for diesel engines to have any chance at meeting EPA/CARB regs. So it was really a cost cutting measure that caught up with the company, costing them more than they ever could have guessed at the time.]
There are no comparable regulations covering hi-fi gear. The FTC ruling is limited to advertising, and does not establish a measurement threshold for the sale of amplifiers. The ruling can be ignored by manufactures if they choose not to advertise power ratings. [FWIW I have read that California wants to set a rule limiting energy consumption of high-end PCs (actually, video cards), but I haven't heard if they are also thinking of banning Class A hi-fi amps.
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Finally, as
@escksu states, distortion in amplifiers is pretty meaningless. Distortion measurements you read at ASR may give you an indication of who is doing good engineering at a price point, but other than that the values won't tell you much else. There are other more important factors to consider than a distortion measurement (build quality, warranty, ease of service, dealer support, manufacturer reputation, aesthetics, form factor, overall power, possibly current ability, and so forth).
From a marketing standpoint, a lot of hi-fi manufacturers don't even care about measuring this stuff. It goes against their business model, so there is no incentive for them to provide specs, much less cheat or otherwise lie about them. Many manufacturers sell 'magic', and many if not most 'reviewers' exist in symbiosis with these manufacturers. The few that are interested in decent engineering will publish measurements for all to see, and those that don't care about it will talk about something else. Each group of customers have their own priorities, and the two usually don't mix.
As far as amps 'going into a special mode' at low power level?. That is actually an old trick. Back in the day Japanese manufacturers were famous for 'sliding' Class A amps (maybe they still make them). Then next year's models would feature something else, new and different, to market. After being in the hobby for so many years it's easy to laugh at it all.