Are Stock Indices Reliant on Too Few?

The Wall Street Journal took an interesting look at whether stock markets are too reliant on a small number of companies, specifically Apple and Microsoft. The Journal noted that the two firms helped power the Dow Industrial’s average to over 28000 for the first time ever in November. Apple shares grew by 66% this year, whilst Microsoft stock soared 47%.

 “With the S&P 500 energy sector trailing the broader market as oil and gas prices stagnate, Apple and Microsoft together are now twice as large as the entire energy group,” the Journal further notes. 

Is this sustainable?