I have heard that with milk, you should drink whole milk and not low fat. Is cottage cheese the same way? Why wouldn't you want low fat? All that saturated fat is bad. It clogs your arteries and causes heart attacks.
To answer your question...the theory is that the nutrients in dairy are not fully absorbed in the absence of fat. The fat in whole milk, or whole cottage cheese helps your body use all the nutrients that are in it.
However, I have a question on top of your question-
I RARELY drink milk or eat cottage cheese by themselves. I normally have cottage cheese and a PB sandwich. Or I have Eggs and milk. If I am already eating fat (from a different source) along with the milk/CC can I eat skim/low-fat and get the full benefits? IMO it doesn't taste bad, and would love to cut out any unneeded fat and cals that I can.