Could Apple be worth $1 trillion? It's conceivable. The $338 billion iPhone and iPad maker is now worth only $4 billion less than market leader Exxon Mobil. Yet its sales have been surging 80 percent a year, and profit faster. And Apple trades roughly in line with the growing U.S. market -- and at less than half the price-to-earnings multiple it fetched in 2006, when revenue growth was much slower.