I'm with Whitey on this. Sort of.
Back when Bill Cosby did that routine engines were carburated, ran rich, and could build carbon deposits in the cylinders if only used for short trips. Modern cars meter fuel far more effectively and in a manner more condusive to complete combustion. And they run hotter. In the '60s most thermostats were 165F, today they're 195F. That increase in temperature was implemented in the early '70s as on eof the early emission reduction steps.
In short, modern engines should not build up carbon as readily as engines did when Bill Cosby did his skit. However, if the engine is high mileage and using some oil, and/or used for only short trips, it can still collect carbon. When an engine is cold, its ECU bypasses the oxygen sensor signal and allows it to run rich until it warms up a bit.
Bottom line: while modern engines are less prone to carbon buildup than the engines of old, they are still not totally immune to it. But if when changing the plugs you discover really bad buildup, or if one plug looks dramatically different that the others, you'll want to check things out, starting with a compression check. It sounds from the post like yours is running normally for a higher mileage engine, but if you're curious you could always run a compression check.