I might be more forgiving of this comic if it were the first time Randall had done the "what would a sarcastic person have been like in classic fantasy situation?" joke, but it's not. And it's not something I am going to stay amused by for long. As commenters on the last post pointed out, not only are there series that do deal with this question (what came to my mind was The Number Devil), and further, isn't a better question "why do they need a 12 year old to save them anyway?"
Anyway, in short, yeah, apparently fantasy novels are sometimes not totally accurate.