I don't actually understand when folks say that girls "go through a pink stage," and that's just "natural." Well, was born back in the Jurassic 1960's. I've been involved in the upbringing of both girls and boys born in the 1970's and 1980's, and I can confidently say that none of the girls went through "pink stages."
Back then, you didn't have the strict gender segregation of toys, games, books or even clothes. Most children's things were in primary colours. Even if it was more common for girls to play with tea sets and boys with trucks, there were plenty more toys and games that were considered socially acceptable for both genders.
I agree that the gendering of products for children is in the hope of bigger sales - two items to a family with a boy and a girl. I don't think it's JUST down to parental or child choice though. The secret of marketing is to convince people they want to buy something they don't yet know they want or need. You create a demand for something and if enough people "bite," then you can actually change the culture of consumption. That is what I believe has happened with products divided so strictly along gender lines.
It reinforces other social messages about what girls should be like (soft, pretty, passive, servile, fairy princesses,) and what girls should be like (tough, dirty, assertive, rough little soldiers.)
And it's seven shades of hell for the kids who don't conform neatly to rigid definitions of gender, from cradle upwards. Thing is, it wasn't always like this. It's a modern phenomenon, created by marketeers. It's certainly not natural and even if it's a "phase," the pressure to conform to a specific model of femininity (and masculinity) remains.