Typical cake ingredients are flour, sugar, eggs, butter or oil or margarine
I don't think I've ever personally made a cake with margarine...? I think it was a big cooking and baking ingredient in the middle of the 20th century
Many older recipes  referred to as "oleo", short for oleomargarine.
I wonder if it does anything to the texture or flavor of the cake. I think butter adds a nice sweet flavor to the batter
butter is made from the butterfat of milk, so may change the taste a bit.
Nowadays, many people make good cakes with coconut oil, avocado, mashed banana, or other vegan ingredients to add moisture. But personally, I think these substitutes are only adequate.
I tend to agree.    Dairy farms produced about 730 million tonnes of milk in 2011
Wow, that's a lot of milk - what country or part of the world was that?
India is the world's largest producer of milk, and is the leading exporter of skimmed milk powder