Not entirely true. I lived in a house that was just over a century old. The framing was exactly what it said it was, a 2x4 was 2” by 4”. Same for all the structure. These were mill cut, but still pretty clean. It was WW2-ish and after that we started to get planed lumber that gave us 1.5x3.5. It wasn’t even until probably the early part of the 1900s that lumber started to become “dimensional”, as in the standard sizes we know of today.