Why this matters: These companies symbolize the central issue of employment in a new age of technology, automation and artificial intelligence. For example, Ford, worth a tenth of Facebook, employs 200,000 workers compared with Facebook's 17,000. Worse, Ford is cutting jobs, saying last month that it will lay off 1400 workers despite record revenues.
Accelerating economic change: The success of these tech giants highlights the changing face of corporate America -- three of them did not exist 25 years ago, and the other two are just 40. That such relatively young companies are on top illustrates the trend of a higher churn rate among American companies. According to consultancy Innosight, the 33-year average tenure of companies on the S&P 500 in 1965 narrowed to 20 years in 1990 and is forecast to shrink to 14 years by 2026.