They're correct, what you read is wrong. What you may have read, and was the subject of a recent thread on this forum was about the 5 wire system. Some of the older wiring, CHANGED OVER TO AC IN THE 30's, existed in the older sections of Washington, DC (and I'm sure other old towns) for a long time. I was involved in the early 70's with conversions of these old systems, but I don't think many were around long after that.
Just another possibility: Are you thinking of radios, TVs etc. which were advertised as AC/DC models?
These were very common up to the 1960s (and into the 1970s for some TV sets). It didn't mean that all the supplies were DC, just that the sets didn't use a mains power transformer and could be run on AC or DC mains supplies.