My point was directed not at hobbyists, but rather at speaker manufacturers who cannot afford an anechoic chamber (ie most of them). In essence they are trying to build a car without a wind tunnel. Any claim about stability at high speed will be on word of mouth ("trust me, I've driven it really, really fast, and it's really, really stable") coming from a financially interested party, themselves. The truth content of such a statement will then depend on luck, not data, and lots of corpses strewn along highways may ensue.
If the motor car analogy seems far-fetched to some, let me point out that price-wise it is often rather valid.
I'm not quite sure how an anechoic chamber relates to the past or current discussion of very low frequencies here, but the suggestion that they are a requirement to produce a purposefully good product is being rather disingenuous to acoustic measurement methods which provide all sorts of noise immunity along with time and/or frequency windowing.
Ironically there's a very nice chamber just over a mile from my office. Shure, it would allow for some much prettier marketing graphs and make certain measurements and quantification more straight forward, but the important relevant data can be obtained and understood without this requirement.
Subwoofers are by far the least complex of devices to quantify. That is not to say that a full description is simply obtained, but rather that the number of variables and dimensions are much less. than that of full range loudspeakers. The fact that more of the information is closer to our grasp is likely why there is such a great interest in boiling low frequency reproduction down to measured metrics. The biggest stumbling point I see is the focus to look at devices entirely in isolation rather than giving much more careful consideration to the environment in which they are used (your room), and to the sensitivities of listeners (ie distortion audibility).