kimchi is fermented vegetables, different spices in the mix to some degree but the biochemistry is the same as what you find in the balkans. just like you say - mostly you can just put some water and a little salt and it works. the little bit of vinegar and a tiny amount of seed yogurt just help things along if you are uncertain about the quality of what is sitting already on the vegetables. yogurt is not as widespread in eastern asia but it's an institution in west asia and eastern europe and biologically the same organisms are involved as with fermented vegetables with variations in specific wild cultures. the wild is the best, but if your vegetables come from a shop you don't know what has been put on it or what that has done to the microbiota.

put it this way, you won't hurt it with a teaspoon of yogurt in a few litres of liquid when making fermented vegetables. as i say, it just guarantees it doesn't go bitter and slimy.