Why would it be illegal to only give money to the winner of one of the competitions helt during this race? It is three competitions in one: Stockholm marathon (open for all), Swedish national championship (open for all that compete for a club that is member of the national athletic federation), and new for this year the Nordic championship, in which only the runners of the national teams of Finland, Sweden, Denmark, Norway and Iceland compete.
Point is, it is not the first Nordic runner of the Stockholm marathon who get's the money, but the winner of the official(!) Nordic championship, which is a competition within the same race. Of course it means in the end that only someone from one of the countries participating in this will be able to get something out of it financially, but it is not simply the first Swede/Norwegian/Fin/... . And what would happen if a Swede would win (maybe unlikely, but possible)? (Hypothetical) Prize money for all three competitions to the same person (don't think there is any for the Swedish championship btw)? Would that be fair?
That's also the difference to the Dutch thing, as far as I'm aware it was only based on Nationality in that one, and not part of any official championship within the race, right?
Newest info is btw that there will be some money for the winners of the marathon after all.
https://translate.google.com/translate?sl=sv&tl=en&js=y&prev=_t&hl=en&ie=UTF-8&u=http%3A%2F%2Fwww.expressen.se%2Fsport%2Ffriidrott%2Fstockholm-marathon-backar-efter-kritiken%2F&edit-text=&act=url