I think people get a bit obsessed about gender because it's one of the few things you can talk about a baby before you know its personality, particuarly before birth. It doesn't (or shouldn't) really matter.
It really isn't very informative anyway, knowing the sex. I mean so it puts your baby into one half of humanity or the other, but there is so much overlap in terms of personality, interests, future careers etc that it doesn't tell you much.
My sister hopes I'm having a girl. The idea is that since she is the kind of girl who likes clothes, pink, make-up etc that she would instantly see a way to bond with a girl. I am a girl (her sister even!) and I don't share those interests, so its a bit of a flawed idea. I'd much rather if she saw that her interests, particuarly her wider ones in acting and music, are definately shareable with the new child, boy or girl.
My husband is determined to get our child (of either sex) interested in his hobby, trains and model railways. ;) I'm sure that I'd love it if our child shared our love of books, and my interests in nature, drawing and geeky computer stuff. But I'm sure that our brain washing enthusiasm will only get our child so far and then they'll discover interests all of their own.
You'll know yourself that your boys are different from one another, a third boy may be just as different again, or maybe a girl would share many interests with her brothers.
I am pretty indifferent as to whether I have a girl or a boy, as their sex tells me very little about who they are and will become. Most people are indifferent about what star sign their child is born under for the same reason.
I guess I would like to have a mixture of boys and girls when we complete our family, though I'm not sure why, just to have 'the experience' of raising both. Of course again that seems to assume that raising one boy is the same as raising another. See how deeply ingrained this gender rubbish is? I would imagine that the comments you have recieved reflect the speaker's own desire realised or not, for that balance of genders in their own family, and they assume you have that same picture in your head of what a family looks like. Thinking of that, it probably is that the picture society has and puts in our head is that a family is a mum, dad, brother and sister.
My mum has been knitting and buying stuff for my new (gender unknown) baby. I asked her if a packet of patterned muslin cloths I spotted at her house were for me/our baby. She said it would depend what colour baby I was having - I laughed and said 'probably white like me and DH' - of course she meant whether my baby was pink or blue (Agbar score? 
) whether I was having a boy or a girl, as the pattern on the muslins was pink.
Its odd that the closer we seem to get in gender equality, the more accepting we are of different sexualities and transexuality (none as much as we could be yet) the more we seem to need to demarkate young girls as pink and floral, and young boys as blue and vehicle/sport obsessed.
Even as babies who all need to do little more than eat and sleep. I mean, does it matter if I use a pink/red patterned muslin cloth to mop up spit up from my baby boy's face and some passing stranger assumes he's a girl? Does that threaten his future manhood somehow? If I wrap my baby girl in a blue blanket (my favourite colour, and the colour of our one and only bedroom) does it matter if she is mistaken for a boy? Does that diminish her future attractiveness (which women seem to be judged upon?). My DH wore a yellow dress as a baby because money was tight and it had been given to his mother before his gender was known - it didn't make him feminine or gay, and if he had been would it matter?
Its a load of gender related, sexist, ridiculousness. Speaking as a woman who wasn't allowed a blue bedroom as a kid, but eventually got dinosaur wall paper. ;) Chances are that whatever sex our baby is, there is a good chance that this little one will be a geek - both parents are dominate in the Geek gene. Poor kid 
Enjoy your boys and your new baby, whatever colour the little one turns out to be