well said. electric stoves would have an effect, not gas ones. unless they mean the electronic ignitors on some gas stoves
and the affordable ups's like apc's only condition power so much. when my a/c kicks in, i still get a pop over my speakers but its not nearly as bad as when dont have the stereo plugged into the ups.
a good line conditioner would make the voltage nearly perfect, and give longer life to your electronics but the argument is a bit like over clocking cpu's. sure it might shorten life, but you wont be using it in 20 years anyway because it will be worthless. if you can afford line conditioners, you probably have thousands in systems that are designed to keep up with technology.