Hi, no they do not pay a discounted price per journey. The train companies in Europe are shareholder of the company Eurail. I don’t know how they divide the money they get from the pass, but they have then a system how much every single train company gets. 

As such yes, but anyone expects that. If not, they would not offer the passes and as EUrail even now more as 60 yrs (EUrail, at that time aimed at travelling USA-often people in the 50ies who had also been in EUR as soldier in WW2), INterRail had last yr the 50 yr celebration.

So I bought a 3 month 50% discount pass, used it on about 60-66 days of the 91, making some 10 different trips out of home for up to 1 week-so no need to carry much luggage. have a off-peak season anyway for home country, so no in/out restrictions. Also used it in HU, where as senior I have free travel anyway, but not for INternat.

Every now and then you can see some blogs where someone has calculated what the trips would have cost if booked normally-most often s/he has then paid less as half of that by using the pass. Also many people will do trips on pass they would not have done anyway otherwise. Normal trains-those without any RES, as even you likely know, most often have enough spare seats. it is these nasty hi-speed lines with their pesky RES that cause the trouble-and loss of income. Hence why they make ti much harder to use those!

There is indeed a kind of key that all the railways participate in to get income divided up to use-in the past this was done by hand that was why you had to send in the passes after use-a big troupe of smart working job students would be collected and make a kind of excel before there even was excel for what countries were used for how many KM. Passes were mostly sold in the north of EUR (SE always biggest per head-it nearly still is) and used in south (IT!)-were fares tend to be much lower anyway.

THis very complicated and specialist work has now been taken over by these mobile passes-that is also the main function of them and the way to use them with trip-reports.