The point of adding lemon is to make sure the PH level is right to invite the correct bacteria, this isn't necessarily Acidophilus. In Nature natural bacteria hang around certain temperatures/plants. So if you live in a spot in India where forever you been making yogurt by adding just a bit of lemon and your daytime temperatures are just right then MOSTLY things work out.
But the smarter way is to start the yogurt with a starter, giving the bacteria you want a head start; once the liquid starts to become sour no other bacteria can take hold.
All this fermentation is alike; I remember reading a pamphlet of a German Beer Warsteiner where the strain of bacteria they use goes back to the 16 hundreds, and some French bakery whose sourdough strain goes back to the 14 hundreds. Some in Belgium they still hang out some damp sheets when a certain flower blooms to catch the yeast in the air for their beer.
Then I saw a pouch on the history channel that was used for centuries to hold a small batch of dried batter (sourdough), in short traveling humans been taking started with them for centuries because you canít depend on your surroundings to produce the correct bacteria.