I've worked most of my life in construction. Most of that in remodel. Many of the houses go back to, oh, about 1906 or so (SF Bay Area).
In old house framing, most load bearing walls have studs that measure 2" x 3 1/2". And also 2" x 2 1/2" for interior non-load bearing walls. Those studs are usually rough cut.
You can buy today rough cut 2x4's. They ARE 2" x 4". Well, more or less. But I'll tell you, so were the old studs I run into--more or less. Full 2x4's are pretty useless in construction; I can't recall the last time I saw any. The standard 2x4 is 1 1/2" x 3 1/2". And has been that for a long time, at least 60 years.
Current 2x4's are indeed planed. But note that the 3 1/2" dimension stays the same as it has for over 100 years.
So. Old 2x4's weren't 2" x 4" either.
It IS interesting that the construction industry went from rough cut studs to planed. As someone who has occasion to touch studs, I'll say I prefer planed. Splinters.