Oh yeah, I've noticed this before. The men have to look smart (though not always with ties, usually though) but the women can wear whatever. I can't remember what it was like at primary, but at the primary school where I do my voluntary work the teacher of the class I work with, who is male, just wears whatever-not a suit. But then primary teachers are generally seen as "friendlier" and a teacher in casual clothing seems nicer, and it's all about niceness in primary schools.
And it's the same with uniforms as people have mentioned. Boys (after primary school) have to wear trousers all year round, however girls can wear skirts. However girls may have to wear skirts all year round, hence get cold in the winter, like at my school.