It's not such a big deal that I think folks need to be putting satin anything down to protect their child's hair, lol. That might be a bit much.
I have little brothers and forget about sleeping, when they get to a certain age where they're more active but not yet strong you'll watch them furiously rub their heads back and forth when they're awake and on their backs creating friction on the back of their heads and breaking that baby fine hair down. But it's good for babies, it's more important their bodies get work and their neck muscles form.
Besides baby hair rarely lasts, when I look at the little baggy with my brother's first hair cut the hair is TOTALLY different in terms of color and texture. I highly doubt even if we didn't cut it the hair would have come out on it's own.
And it's all babies, not just blacks, I see it with plenty of white babies.
That's a good point about the baby hair not lasting, anyway. My son's hair was bone-straight for his first year of life, like slick type 1. By the time he got his first hair cut at 2, he had curly/wavy hair that was a little coarser. I guess his hair transitioned during his second year of life. I wish I could post a pic, but I don't have any digital ones.