I'm going to go with it just depends on the age difference, the dynamics, etc... My sister is 6 years older than me, so we aren't really close but definitely keep in touch, get along fine when she visits & have a good time. She lives in another state than I do, got married at 19 and moved out of state I think by the time she was 20 and has lived out of state until this day (various states), I was still in High School when she moved, so obviously we wouldn't be as close as siblings that lived together, etc...
My brother is 3 years older and we played together more. He lives locally and we are closer than my sister & I but I think proximity has a lot to do with it. Much easier to hang out for holidays, kids' birthday parties, etc... when you only live within 20-30 minutes of each other.
I don't remember my parents doing anything in particular (as a matter of fact, I remember my brother & I being rather pesky to each other growing up at times! ROFL!!! I also remember being the youngest that I was a pest to my sister when she had friends over. What was funny is my best friend is an "oldest" and her little sister would be a pest to us but it never really bothered ME but drove my friend insane! - They get along fine now!).
I have 4 kids and my oldest 2 at the moment, get on each other's nerves but DD adores the 5 year old and the "baby" but I know the age gap will be big as there is a 10 year age difference between the oldest & youngest - so when she turns 20, he will be 9 1/2. It will be a completely different dynamic between those 2 and the 2 younger ones who are only 3 years apart!