There is a graphite based coating for spark plug threads that will allow electricity to conduct, but withstands heat and works as a dry lubricant so the plugs are easy to remove later.
BTW, my 2009 Chevy Equinox has no user maintenance for the transmission, and has an electric power assist for steering, so the only fluids to be checked are engine oil, coolant, and brake. The dealer does the transmission fluid check once a year. The spark plugs are platinum tipped, so they don't accumulate carbon and don't need changing for a long time.
GM is reducing maintenance costs by designing better components and having longer periods between changes. This is why GM vehicles get better each year.