MetalMagpie said:
One thing I still don't understand: Why is designing characters to visually appeal to men sexist?
Sexism is something like this: Women shouldn't be paid as much as men to do the same job, because they aren't as valuable.
There's more to sexism than that, particularly when you look at media. Women are frequently/usually portrayed as objects to be seen by presumably heterosexual males. This is often referred to as the "male gaze" (I personally don't use the term much since it doesn't mean much to most people). This pervades videogames, where women often are designed to be eye candy, while men get far more varied representation (when's the last time you saw a male videogame character posing suggestively?).
The fan service in Skullgirls wouldn't be sexist if the game existed in a vacuum, but it doesn't. Sexism in general doesn't exist in a vacuum.
Also, there's the Gender Games video from The Big Picture on this site that concisely explains the presentation issues videogames have.