In japan they have segregated anime and manga into shoujo/shounen, girl/boy.
Does this increase sexism and enforce gender roles, or is it a way to appeal to both sides at the same time?

It's clearly reinforcing gender roles. By making a show 'for boys' and not girls (and vice-versa), you're setting up different expectations for the audiences. This holds true even if the company is spending the same amount of resources on stuff for the opposite genders. Same story with toy companies. Hell, clothes companies too.

It certainly is a way to appeal to both sides. But perhaps it is more interesting to ask whether it's effective compared to the alternative: producing universal content aimed at no specific gender. That's hard to judge. You can't run a controlled experiment. But you can infer from some theoretical considerations. It's a given that presently, gender roles in children are quite well established. So girls and boys actually, generally, have different interests. Therefore targeting those markets specifically should yield profitable results. I've skipped some steps in the logic, but I don't think my suppressed premises are too controversial.

So, with that established, you may find it more interesting to ask whether it is ethically correct to target girls and boys with entertainment based on gender, whether gender roles can be effectively eroded with entertainment-propaganda, and the desirability of doing so, etc.

So, pixel art!

How sexist would you say the oeuvre of prominent pixel craftsman Paul Robertson (nsfw) is?

(Damn, I wrote more than I had really intended. What I mostly really wanted to do was just post the above link. Make sure you go though all pages, 5 or so total!)