Let me be clear: I am not asking about their applications. I know some really good recipes where you use one or the other. I know you can replace them with each other in some recipes, not in others. That is not what I am asking about.
My question is about how they are different in their constitution. I have read that to get sour cream you ferment cream with a few different subspecies of Lactococcus lactis. Sometimes rennet or acid (lemon juice or vinegar) is used, but authentic sour cream requires the fermentation with bacteria (which converts cream's lactose to lactic acid). When I look up recipes to make cream cheese, I get the same instructions. You take cream, again you ferment it with a couple subspecies of Lactococcus lactis, you strain it to get rid of the water, and you get cream cheese. The only difference I see is that in the US, sour cream usually has a 20% fat content, whereas cream cheese has a fat content of 33% or higher. The other different thing is when making the cheese, "sometimes" some milk is added.
But this cannot be the only difference. Otherwise we would not call one of them cheese, and another of them cream (considering the fat content, even those names seem ironic). I would appreciate if someone can shed some light and give some insight.