Not sure how much is being adopted and how much is having no parents until you were a year and a half. My niece was adopted at birth (placed with her permanent family at 6 weeks and in a loving foster home before that) and has known all along that she has a birthmother and a mommy. She is as typical 10 year old with typical "growing up" issues with her parents - whom she loves very much. She was lucky. Babies feel love - or the lack thereof - well before they know how to express it or remember things. Experiences from that early in life build the foundation of later emotional identity. What happens later can either intensify that or, usually with a lot of time and work, can create a more stable foundation around the original one.

In short, I don't believe being adopted causes detachment, but the experiences in life surrounding the adoption issues can easily take one down that path.