I do not believe this is true.
I started cooking with various cast iron pans about a decade ago - initially I was dubious, and it took longer to season in the Lodge than the Le Creuset (both around the 20cm size, normally used on gas). Now they're equally seasoned, and cleaning is typically some hot water, ideally the same night they were used, maybe a very mild detergent, with a nylon scrubbing pad. If I don't get to them until the next day, I may need to run some hot water over them for five minutes, but that's rare.
OTOH I've got a number of non-stick coating woks, that I treat with great care, but are (in the same time period) looking a bit crusty / scratched, despite only using silicon / plastic / wooden utensils, and never running them above a medium heat. That is, treating them much more cautiously than I treat the cast iron.
Granted, I don't do, say, omelettes in a cast iron -- but herb encrusted meat, at very high temperatures, which would challenge a non-stick (teflon or similar) takes about 30s to clean out of the cast iron if I get to it later that night.