I can't speak for anyone else, but I can explain why I still nurse past a year. I hope this doesn't come across as offensive because I don't mean it to be. I just truly want to answer your questions.
Yes its true, my son doesn't need breastmilk to survive like a newborn does since he is eating lots of different things throughout the day, but it is recommended that he have 12-20 ounces of milk or milk products a day to provide the appropriate amounts of calories and fat that he needs for a balanced diet. I feel that if he needs that much milk a day until age 2, it is safe to assume that nature intended that he have my milk until then. Cows milk is a luxury of modern society. Of coarse there is nothing wrong with giving cows milk, but it's not the way nature designed it. Not to mention all the antibodies that are also present in breast milk.
Children also have a biological and developmental need to suck, also until roughly age 2. It helps release feel good hormones in their brain. My son does not take a pacifier and if I were to stop nursing I would be taking away a major source of comfort for him. He not only relies on breastfeeding for the milk, but it instantly resets his behavior. He nurses to calm down, when he is hurt, when is he tired, and it always helps him feel better when he is sick or teething. Many kids have pacifiers until age two or later to substitute for this instincual need to suck, or breastfeed. There is nothing wrong with pacifiers, but again, its a modern invention/convenience.
I co-sleep and night nurse because its easy and its how we have gotten the most sleep. I continue to do it because at this point he is used to it and at least I know he is getting the appropriate amount of milk from me. One day I will night wean, but I'd rather do it when I know he can handle the change. I'm OK if it happens slowly. I cant say one way or the other yet, but I have actually heard the opposite is true in regards to attachment and dependency- that the more attached they are as babies and young toddlers, the more confident and independent they are later. As I see my son's personality unfolding, I would think its going to be true for him.
I hope this helps. I know nursing past one isn't for everyone, but nursing my son today feels just as natural (if not more so) as it did the day he was born.
Also, I didn't always feel this way about breastfeeding. I used to think I'd stop at a year, then slowly I started looking at it differently and that has evolved to how I feel now. It feels natural to me, but I know not everyone shares those feelings, and that's OK too.