It's only sexist if you're going out of your way to look at it like that. The game's target audience is, obviously, twelve-year-old Japanese girls. Think of it like this: it's not so much a portrayal of a typical woman as it is a portrayal of a typical magical princess with a magical umbrella in a magical kingdom where mushrooms are widely considered a higher form of life. (and magical!)
I mean, come on, the Marioverse isn't supposed to be taken so seriously. "There goes Peach, your typical over-emotional woman. There go Mario and Luigi, your typical plumbers who travel by warp pipe. There goes Koopa, your typical evil turtle overlord."
...By the way, what's the deal with the faces/heads in today's comic? No offense, but they seem a bit... off. O_o