I am going to have my 3rd child in October, almost exactly to the date 2 yrs from when DD was born, and 12 yrs after my first. We did it this way on purpose. Before DD was even conceived we knew we would have her and 1 more, very close together.
For me there are 2 reasons... 1) my sister and I are about 3 yrs apart, and were always just far enough apart that we did not ever have the same friends. Yet close enough that we fought over toys/clothes/etc constantly. We never got past that either. We barely speak at 30 yrs old and 27 now. My DH and his brother were a bit closer in age, and they got along famously as kids, because they had the same friends, IMO.
2) I have a 12 yr old boy, and having another baby so long after he was born was very tough on me. I had thought I was done until I met DH (DS is from a prev marriage). Starting over after 10 yrs is very difficult. I have trouble making both DS and DD happy because they want such different things all the time. I would love to take DS to the movies but we cant because DD is too young (and I'm not that mom who's kid cries in the theatre). I love playing w/ DD and watching some of her shows with her, and DS gets frustrated and annoyed with them because they "dont make sense". There's just a laundry list on both sides of the fence w/ them that we cant do easily or enjoy doing w/ one because of the other.
I dont think I do a disservice to my daughter by giving her a sister at 2 yrs old. I'm suprised someone would make that suggestion, but MDC is full of ...vibrant personalities.