The social aspect and immune system points are two that get over-looked a bunch. Friends of ours took their daughter to a home day care. They would make little comments about not having to take days off due to their daughter being sick like we did. Once they hit kindergarten, their kiddo was constantly coming home with something. It sucks to see kids sick, but they need to be subjected to some of it.
We really benefited from a center because it helped my daughter understand what was appropriate behavior when it comes to things like lining up for lunch, respecting other children's things and personal space, as well as being on a more class-room style of time schedule. My daughter also interacted with some special needs children. It did a lot of good for her to have that interaction as early as possible. It allowed a safe environment to ask questions and become more understanding of others. She also learned not to take some things for granted.
I don't want to paint with a broad brush. There are some fantastic educators running home day cares. There are also some horrible people in daycare centers (those stories piss me off).
We were limited by not having family around us to help out and not really knowing a good home day care provider near us. It was a ton of money, but I'm not sure I would have made a different decision looking back on things if I had other options.