Arcing power lines can be tracked down with with a shortwave radio and reported, but the powerline adapters are a nightmare. They're suppposed to notch out the amateur radio bands but many do not, often swamping everything from 3 to 30MHz with noise.
That said, I think that these devices are actually quite rare in the real world - most people don't even seem to know what they are - and in my testing the noise dissipates very quickly as I leave my house, disappearing into the background of the city after only 20-30 feet.
I think that regulators have definitely dropped the ball on HomePlug, but I also don't think that it's that much of a problem, particularly given that it's been a commercial failure. Most of the ire towards HomePlug comes from people being upset about commercial-scale BPL installations, which actually have the potential to be a major problem over a large area.
In my house, my monitors actually account for more problems I experience than the HomePlug adapters do, in my everyday radio usage. And they aren't even cheap knockoffs, they're pricey name-brand models.
In PLC (power-line communication), wiring is not meant to act as antenna. All transceivers are wired. It's an undesirable, unintentional side effect of limited (to the extent of complete lack of) cable shielding - because, well, power lines are usually meant for different application than data transfers.
Wouldn't ethernet cables have the same issues? Does the increased power flowing through power lines somehow amplify the signal? Is that pretty much the definition of what a power amplifier in a radio does, add juice to a signal on an antenna so it gets broadcast further?
Does the amount of wattage going through the line effect how "loud" the interference is?
Interestingly enough, there is enough radiation that you don't really need an actual connection. Someone put one of the endpoints in a field with a generator and got a connection to another endpoint. In a sense power line adapters are just using radio over the air.
Sending data over a power line, even at low bit rates is very difficult to do reliably. So all the radiation is in a sense a feature in that it improves connectivity. Not so much a feature to those who have an actual licence to use those frequencies...