The Lego Friends theme doesn't have firefighters because it is focused on social relationships, not overcoming conflict. It doesn't have to be a girl vs boy thing (although it is undoubtedly targeted toward girls to compete with other non--confrontational toys that have proved popular with girls), it is just part of the theme. Ninjago doesn't have firefighters either.
I think it is great that Lego has developed a theme that isn't focused on physical confrontation. I have three girls who play with Lego and they request a mix of sets. For Christmas, they requested sets from Friends, Lord of the Rings, and Ninjago. My four year old got a Chima set. They don't see it as a girl vs boy thing.