I think this is more a philosophical question than a serious one.
I would imagine that if you go back a hundred-plus years when centerfire cartridges were going in to production, there were probably legitimate concerns about sending a proper flame in a cartridge with a much larger physical diameter than the smaller cartridges of the day.
Today? Probably not a big factor. But it has been that way for a long, long, LONG time and change doesn't come easy.
We still call them ".38 specials" but nobody is too upset that it's not .38 of an inch diameter. It's called this because the cartridge evolved from a heeled bullet round where the bullet diameter was larger than the case and sat on the outside of it. Not the other way around like we do it today.
To sum it up--they probably could very well use modern primers to ignite all cartridges across the board. In fact, if every cartridge used a small primer size, everything on the market could probably be properly ignited by a small rifle magnum primer. The problem with the idea is that a hundred years of load data built around smokeless powder and the cartridges for it would have to be scrapped and re-worked from scratch so nobody was out using faulty data meant for old primers. Also, all brass with large size primer pockets in existence would have to be relegated to the scrap pile and new brass produced. All the stocks of non-mag and large size primers would have to be tossed out. All the tooling set up to build large primers would be useless.
That would make no logical sense whatsoever.
It would also make no logical sense to avoid buying a slick new .45 auto because you'd then have to stock a different size of primers which you can pick up (even at a lousy price) for $30/1000.
