Well shoot, I break that rule all the time, I like Shojo sometimes, but I like Shonen most of the time, I'm a tomboy. Anyway, it is easier to find things that are separated by gender for some. I have seen girls staring at me when I read Hellsing and they tell me its for boys, but when I tell them I'm a tomboy, they are always assuming I'm into girls, lol, what a laugh. i just think it is funny that when you're a kid, your parents are the ones who tell you, girls wear pink and boys wear blue, which is really sill.y If I have a kid, I'm going to dress them in what fits.
Its the same for manga, its the person's personality the picks what they like to read, regardless of the gender. Sure I will pick up a girlie one every now and then, but I will read the manga that i feel happy with. So i sort of expect the same for most girls who think about it, I know guys who like girl manga and also Yaoi if you believe that. LOL.