in a discussion a few months ago my dad was talking about his will, and how everything will be divided equally between all of us, but then casually added "well obviously your brother gets a bit more because he's the oldest and your sister gets more because she is the baby of the family"
now, if there were 5-6 of us i could maybe understand - or if there were 10 years difference in our ages - but there are 3 of us!! and we are all only about 2 years apart!
i actually had to point out to him that what he is actually suggesting is that I am left out because i am in the middle - he hadn't even thought of it like that - he just had this in-built idea that the eldest and the baby get special treatment.
he was one of 8 siblings
so yes it does affect people, even if only because the parents have this in-built unfair notion of birth order labels and adopt them without thinking.