It may seem unbelievable to those of a certain age, but comic books are not terribly popular with today’s youth. Still, comics are a $500 million a year industry, with some savvy marketers behind them, and this coming weekend, “for the fourth year in a row, stores across the United States, England, France and other countries will be giving away 2 million comic books” in an effort to get more of us hooked on the increasingly diverse genre.