I think if you have all girls, people tend to assume it must be sad for the dad for being outnumbered. And if you have all boys, people tend to assume it's the mother that is sad because people assume mothers want to bond with daughters and the whole future daughter in law taking your sons away thing. Those are stereoptypes of course. I think that is why in our society, everyone assume everyone wants mix gender families.
ITA with that.
And to the OP, I agree with you that the comment was insensitive, regarless of why she said it (genuinely happy or trying to hide disappointment of not having one of each). I have been on the receiving end of similar comments from a "friend" of mine (who has two girls and for whom having had just one boy seems like it would have been a disaster) so I know how you feel. Saying how one gender is so much better than the other to a person who has kids of the "lesser" gender is a big no-no to me. If not downright mean, it shows a lack of respect, sensitivy and consideration for the person's feelings and kids. Heck, I personally would never even tell someone I dislike the color of their sweater (unless REALLY asked for an honest opinion), so I resent anyone making such comments to me, esp. regarding something as important as my kids. I think this goes beyong GD too - yes, having GD, perhaps we take those comments more to heart, but even if we didn't have GD, the comments would still be hurtful IMO.