Here's something from ARRL:
Even if measurements are made correctly at 30 meters, the absolute maximum limits in the Part 15 rules are high enough that harmful interference is likely. Those S9+ level signals from otherwise legal Part 15 radiators would cause harmful interference to almost all received amateur signals.
Although a manufacturer is responsible only for meeting those limits, in many cases, they end up assuming some responsible for harmful interference on behalf of their customers. As a minimum, there are very real costs associated with dealing with interference complaints, and as word of mouth about widespread interference spreads, it could well have an effect on product sales.
Many trade associations for similar products have recognized the need to offer additional protection to radio services that might be found near their products. For systems deployed in residential neighborhoods, it is quite likely that these systems will have nearby amateur radio operators.
Over the past few years, ARRL has worked closely and productively with several of these organizations. As a result of joint testing performed with ARRL, HomePlug has chosen to include a spectral mask (notches) in the HF ham bands. (There were a number of amateurs on the HomePlug working groups who well understood why it was in their employer’s best interests to avoid widespread interference from their products.)
Although there is still some potential for interference, the specification has reduced their signal levels in the ham bands about 30 dB below what is required under Part 15. HomePlug chose to add the spectral masks to avoid the potential for widespread harmful interference to Amateur Radio in areas near HomePlug systems.
It seems evident that we must now create a similar problem for these manufacturers. It is NOT OK to shift the problem onto other radio services that aren't as well organized. We need this technology OFF HF!