How do typical developing siblings cope?

Q: how do typically developing siblings of a child with Down syndrome cope in life?
A: I have been told that often siblings feel left out because more attention is paid to the child with special needs, I've been told to have more children so Arthur doesn't feel like this, I've heard that siblings of a child with Down syndrome are more caring and compassionte people, and that they are protective of their sibling with Down Syndrome.
I need to do some more homework on this but I found some links that were interesting, one talking about how families are impacted and what makes some fair better than others, and then a very interesting article about what the 'sibling whisperer' has to say....I liked this article so am posting the link first and then the other one.

http://www.sheknows.com/parenting/articles/981881/siblings-of-children-with-down-syndrome

http://www.down-syndrome.org/information/family/overview/?page=3