Of the three Mr Mankiw proposes, only Steve Jobs plausibly had an irreducible, unique effect on material culture and the structure of an industry. Mr Spielberg and Ms Rowling are acclaimed artists, but their startling wealth and prominence are entirely due to the increasing power of network effects in mass culture over the past several decades. Mr Spielberg happened to be directing his first movies just as Hollywood was beginning to stage coordinated marketing blitzes that created round-the-block lines for top-grossing films. Ms Rowling hit the bookshelves just as a similar superstar phenomenon was taking over publishing, with sales increasingly concentrated on individual mega-bestsellers rather than spread across a few dozen authors and titles. Mr Jobs is an unusual figure in that his ability to combine engineering, aesthetics, and a vision of how users might interact with the digital universe has created a kind of integrated multi-product entity that might not otherwise have existed; it's not clear that BlackBerry, Nokia or Samsung would have been up to the task. But even in Mr Jobs's case, much of the power that accrued to Apple was due to the gradual sorting of the consumer information-technology world into integrated ecosystems