I saw it too, it is pretty odd.. maybe the women who post that wanted that for themselves? I was the youngest of 3, my brother was 8 yrs older and my sister 4 yrs older.. oddly I always wanted a boy first so if I had a girl she would have an older brother, since I so adored mine when I was growing up.
I have a 4 yr old and 2 yr old boy now and am having a third son. I always wanted 3 kids and I wanted 2 boys and a girl.. never thought of the brother/sister, sister/sister, brother/brother relationship at all really.. but, i can say, that anyone I meet that is having a second boy I tell them how awesome it will be for their older one. My 2 boys are incredible friends. My older son protects his little brother like there is no tomorrow and they are so good with playing with one another and sharing.. they just "get" each other. I picture they are going to be friends for life. Their personalities are pretty different. Our older son is pretty intense with moods etc, and our younger one is just so easy going. So they compliment each other well. I did want a girl a for them too to have a sister experience.. but, I think any relationship you think your children will have with one another is just that.. something you "think" may happen. You really can't predict how they will get along. In fact, the moms I know with 2 girls around my boy's age have a much harder time with them getting along.. they have a lot more jealousy issues. When I was growing up, I couldn't stand my sister! She was always ordering me around. I'm close with her now, but wasn't a party when we were little.