I've seen houses built in the late 1960s that used non-standard 2x4s, so I will dispute those facts. I don't remember details (and can't be bothered to look them up), but IIRC several different standards were tried before the current one finally took.

The pre-planing is a common claim, but I don't believe it. They can make lumber whatever size they want - of course they need to plane it, but they just make it larger to account for that. Still the planing excuse it one they like to use because it doesn't show "them" as trying to cheat us.