Gosh, I did not open a grammar book since I was about 12! It's unbelievable that the Russian grammar is so hard that they need to continue teaching it all the way through school.
There can be two causes. The first is that Belorussian ministry of education thinks it is necessary for their people to know what types of subordinate clauses are in Russian, and Swedish does not. The second is that Russian spelling and punctuation are based on grammar, as I mentioned before.