The pdf that you were mentioning was something that Bill Peters threw in to the files with several of his later titles ('later' meaning since 2009). I am guessing, although I can't prove it at this point, that this was also put together from the artwork created for the game. What I mean by that is I am not sure how large that the original artwork was -it might have been bigger than what was in the pdf, or at the very least, probably less lossy (just a suspicion).
Anyway, you got me curious now, I am not sure what it is that you would do with this sort of thing?
... resize it to your own liking -I guess you can kind of do that already in Austerlitz, Leipzig, Bautzen, and 1814 - no idea where you would find others (I will qualify that to mean 'others' being larger versions of what is used in the stock graphics).
You are right, though, the name of the game is the ability to re-size... It can be the same thing with some of the huge versions of maps -Quebec from FiW was a great example - that thing -I swear that it was made out of something like 140 screenshots of 1600 x 900 px (actually those might be larger than that since I think I actually took them on my desktop which has something like 2200 px on the wide side of things.).
Now -part of the resizing when it comes to maps I am pretty sure are caused by artifacts of 8 bit bmp files... can't prove it (won't prove it with the Quebec map ... not going to mod it and then take all of the screen shots again simply to see what happens ...) -thing is that it works in reverse when creating enlargements - where things can become badly pixellated.
Ok too I find the 4k monitors thing interesting, but I guess the thing to keep in mind is that this is not really the day job for anyone at JTS -certainly not Tiller himself -nor anyone I know there ... I am not sure how far that extends out too - but I also don't want to come off like I am not interesting in seeing what you can do in circumstances like that ... but yeah if you go that far- why keep it as a bmp when you can switch formats (even in keeping with the same style) and use pngs.... just a technical statement and something I learned while working with graphics ... certainly not anything I heard anywhere within the company itself...