i don't know if it's so much that ninjas are over-used in comics or that ninjas just tend to sneak in. i'll bet half the time the cartoonist doesn't even know he's drawing a ninja untill it's too late.
i have no explanation for the robots, i would just assume they are taking over. as for pirates, it's true that they arn't always as sneaky and cleaver as ninjas, but what they lack in stealth they make up for in brute force and monkeys. many a cartoonist has met his death at the hands of a pitate whom he refused to add to his comic.
This is true. I blame the rise in the web's monkey population on pirates, who rarely check their beards for signs of nesting.
I often wonder if the ninjas, robots, pirates and, by extension, monkeys have formed some kind of coalition to take dominance of the Internet beginning with webcomics and working their way, for want of a better word, up. It will not be long before they will control our news outlets...
Perhaps now is a good time to invest in an anti-monkey bomb shelter.