No, and they rough cut fast closer to 6/4 (1.5") than the original 8/4 (2") they may have originally used, because we don't care about the quality as much. Part of that is the wood isn't as good. Part is our machinery is now more precise.

To get a 1" finished board you need to start with at least 5/4, because you may have some twist in the board and you can flatten alternating sides to make it flat. If you were just running it through a machine without paying attention, your might need to take that same board down to 0.75" to get it flat.

But they aren't wasting time like that for framing lumber. But when your lumber is expensive, it's worth a little focused labored to use more of the board

That is some of it and it varies a lot based on the species, though I'm a lot less knowledgeable there.

In the hardwoods I usually work with (walnut/maple/padauk) its fairly minimal. A nominally 4/4 board usually comes in about 1/16" small; which is a lot less than I lose running it through the planar. Some of that could be the sawmill skimping out too and cutting just a bit undersized....

I'm finding quoted numbers between 2-8% volumetric shrinkage (https://www.wood-database.com/wood-articles/dimensional-shri...), which is still quite a bit less than you find in the small dimension of a 2x4 (2"-> 1.5%, or ~33%)