Don't know how important it is but a .38 spl. brass is about .38"
that's a key part of the story. Early cartridges were loaded with "heel type" bullets (like the .22LR still is) where the wide part of the bullet was the same diameter as the case. So the early .38s" actually had .38 caliber bullets, the same size as the outside of the case. The .44s were the same way. Later on, when the bullets were changed to the inside lubricated type we use today, the bullet diameter was reduced to fit inside the case. SO the .38 bullets became .36s and the .44s became ,43s.
At first, the bores didn't change, as the now slightly undersized lead bullets used upset well enough to seal and be accurate.
Later on, bore sizes were reduced, as well. Cartridges developed later that never used heel type bullets always had the smaller bore and bullet size, but kept the old caliber names, because that was what people were familiar with and expected. That's the reason, in a nutshell, though I left out a lot of details.
In rifles, .40 caliber and above are big bores, so I think its a fair spot for pistols as well.