He explicitly mentions stick figures that can be better than photorealistic painting as readers of xkcd might agree.

But take the Scott Pilgrim stories, everybody looks mostly the same except for hairstyles. I remember there is also a joke by one of the characters that everybody looks the same anyway.

I'd say, these are suggestions and not hard rules. You might get away disregarding some of these.

On the contrary, I think he might agree with the characterization. It is a hacker's comic after all.