I can think of one situation why Purifi specs the way they do, via the power curves. They leave it to the end-user/manufacturer to determine the power and distortion specs of their end product. I could spec 100W/Ch @ 0.0001% THD+N ... another vendor could spec 250W/Ch @ 0.01% THD+N ... and yet another could spec 350W/Ch @ 0.1% THD+N ... and they would be ALL CORRECT if they are using the same module. In hindsight, this is a clever and flexible way Purifi gives them this kind of flexibility.
This has always been the case. Except you seem to be so stucked at FTC regulation.
To quote from a TI's document:
'There are a few standards that describe the power rating of an audio amplifier. The Federal Trade
Commission (FTC) establishes fair advertisement practices for home audio power ratings. This is
described in the FTC document 63FR37233, 16 CFR, Chapter 1, Part 432. Another standard is the
Electronic Industries Association (EIA) SE-101-A. For the car audio industry, some manufacturers accept the Consumer Electronics Association CEA-2006-A standard. It defines how the amplifier should be tested
for power and signal distortion.'
So there are different standards and regulations to be used. FTC is mainly targeting at "advertisement" instead of actually specifying the amplifier. So that no false information is used. The well known erroneous Watts RMS unit is from this regulation.
I have yet find documentation on SE-101-A. From my source it's mentioned as being old and non-active.
CEA-2006-A is relatively newest and most widely accepted standard for standardized testing. The well known 1% power rating, A-weighted SNR etc are from this standard.
There are more information on this site if you don't want to buy official document.
http://rftech.custhelp.com/app/answers/detail/a_id/199/~/cta-2006-(cea-2006)-amplifier-power-standards
To be fair, the final solution is just to publish as detailed measurements and tests as possible. There's only so much information that you can squeeze in one sentence. Don't say average joe or layman can't understand it. Then why do we expect them to understand anything at all. All data is published it's up to the customer to learn how to read the specification and decide what's suitable for them.