I believe that attachment and well being later in life are both effects caused by your biology. Therefore a child with good attachment is just indicating his natural ability to have interpersonal skills later in life.
I agree that biology may have some basis in attachment styles and later success. There may exist a genetic predisposition toward attaching to the parent in a certain way, and this predisposition may also have a bearing on a child's later interpersonal skills. However, I do think there are environmental factors that would definitely have some bearing on attachment styles and later success, such as interactions between the child and parent.
