Dzien dobry. Just back from there too-last week half a day going from Wroclaw to Vilnius/LIT (by overnight bus from the west station).
Was there first time in ´75-communist, visum needed, change real money for printed notes etc. And at that time this east-west train tunnel had just been opened. That stalin´s revenge-the skyscraper, by far the only high building all around.All trains by PKP, the giant state institution.
There has always been a distinct separation between OSobny= persons trains and Poszpiesny=fast (now IC), As you may have noted-but Srodm is under giant renovation with many trains diverted, these use Srodm and Centralna there. BTW: this is the only station named Centralna in all of PL, all other main stations are named Glowny=main. (HBF in german). Except for some stops in the Gdansk area-where the OS are 3d rail and thus separate anyway, this is unique in PL.
You will not want to know how much passenger nrs have declined in PL on PKP-even though there is an upward trend again now. The nrs at that time-plus the nr of trains and the need for space for all services then-selling tickets, checks etc. were so much higher that it could not be provided in 1 stop-plus that the general view at that time was that demand would ever be rising in the glorious optimism of people´s republic. Also remember quite well that many Posp. and INTernat. trains needing more time to stand at stops did not even serve it, but the northern Gdanska. And there was not a sign of metro or other fast mass transit then at all. Those few pax needing to change from OS to Posp. could do that easily at either east or west.
I think there is even a wiki-item on this, but only in Polish.
Very soon after PKP split up into a basically commercial IC-branch and subsidised local PolRegio branch, many regions split off, as did the one here into Koleje (=railways) Mazowieckie. But then, as seems usual in PL on that, a struggle came between city and region on payments and on the quite busy inner-city sections SKM started to offer additional service to strenghten- named SKM and in red+yellow livery.
People from 70-any, not just EU, enjoy free travel in Warszawa, also on these local trains. Just show ID when there is the sparse check. Also all normal urban tickets are valid.