I agree there is so much more to know about a person rather than boy or girl and as a society we are too focused on boy or girl behaviors, but by not telling people what the baby is it makes it all about the gender issue. When you a meet a baby you typically know the gender either by name or dress or other parental clue-in and once that is out of the way, then you have the opportunity to learn their favorite toy, how they like to be held and whether or not they like applesauce. By withholding that gender identity, the focus is totally on boy or girl because as humans we like to compartmentalize.
With Milo we've tried to walk a middle line in the gender issue. We didn't find out his gender before birth so for the first several months of his life he wore a lot of green and yellow, but he is now rocking out golf shirts and little boy shorts. He is allowed to pick out his toys and activities. So blocks, cooking things, tea sets all get a thumbs up from him. Cars, trucks and army men not so much. Recently at a store with a giant display of backyard play balls, he picked out pink as the one he wanted to take home. I hesitated briefly and then went with it. We now also have a purple ball. Both are typically girl colors, but a boy toy. Regardless, we have plenty of fun chasing then around the grass.
It's sometimes a tightrope walk this bringing up a child in a gender-crazed society. As parents we want to allow for freedom, nurture a healthy identity and provide the message that boys and girls are equal. We also want to make sure our children are happy, well-adjusted and accepted for who they are. Whoever that turns out to be, because there is more to a person than gender.