The lack of breadth as well as the underperformance by the Dow transports could be a signal that the market rally could be sputtering out, at least for now.
Julian Emanuel, executive director of U.S. equity and derivatives strategy at UBS in New York, said the weakness of the S&P 500 and Nasdaq on Wednesday versus the strength of Apple shares showed an "underlying fatigue in the rally."
The S&P 500 and Nasdaq Composite traded flat on Wednesday, even as Apple jumped nearly 5 percent.
Naeem Aslam, chief market analyst at Think Markets in London, said the Dow milestone was "a remarkable thing for investors ... but at the same time, this could also be a trap if the momentum does not follow."
Aging Bull
The more than eight-year-old bull market in U.S. stocks got a second wind after last year's election of Donald Trump as U.S. president, on expectations that his business-friendly policies including tax cuts and deregulation would boost corporate gains and economic growth.
But tax cuts and other parts of the Trump agenda have not materialized, leaving earnings growth as the real engine of the market.
"Earnings growth allows the market to be patient about Washington. It allows the market to be patient about fiscal reform," said Steven Chiavarone, portfolio manager at Federated Investors in New York, who said they would "be buyers on any weakness."
Fundamentals remain strong. With 350 of 500 companies' reports in, the S&P 500 index is on track to post back-to-back double-digit quarterly earnings growth for the first time in almost six years.
Still, the market is expensive by historical standards. Investors are paying $18 for every $1 in expected S&P 500 earnings over the next 12 months, near the highest since 2004 and above the long-term price-to-earnings average multiple of 15.