That's exactly what Apple is trying to do here. It happens all the time, sometimes over the course of just a year or two (see: netbooks) and, while companies have made billions by establishing truly new categories, rarely has anybody rocked the world by splitting the difference between two very closely aligned ones. Product categories come and go, grow and wither, revolutionize the world and then slowly fade into a state of cold, quiet, everlasting obsolescence.
