True. The plan behind the yogurt or other medium is to get a certain kind of moss growing while precluding other growths. A non preclusive medium just left out for random spores is going to grow the most opportunistic, molds and fungi, before moss can get going. Yogurt works pretty darned good in that it makes a credible glue, resists a number of molds due to the nature of the beast, and looses the undesirable odor within a few days.
not sure if you have ever set up a dart frog or other planted vivarium, but fungi and molds are really not a big issue. molds form whether you use yogurt or not (i have done both methods) but they disappear as soon as the nutrients is used up and the moss begins to grow after that. and to target a certain species of moss... all you have to do is get that particular species spore and provide the right ph levels and temps. i have successfully grown many species of mosses in vivariums from temperate and desert species to tropical species. some prefer alkalinity. some prefer acidity. others do not care. some prefer only growing on rock. others prefer only growing on wood. others prefer only soils or clays. it all comes down to proper medium, proper lighting, and proper temps... even then... many species gradually adapt to a change in temps. it all comes down to what method you prefer as both can work just fine... i prefer to stay away from the yogurt method as it doesn't work with many species of moss.
HAHAHA!!! it's crazy how well moss grows where people have urinated. When I lived in washington, some friends and I had built some really nice dirt jumps in the woods (we ride freestyle BMX) and everything was green out there except the jumps.... We would pee on the backs and sides of the jumps to encourage moss growth. It worked very well... so well that you could pee a pattern or your name on a jump and the moss would grow 10 times faster on the pee trail and you would even tually have your name or whatever growing on the jump... strange but true...