The S&P 500 index (SNPINDEX:^GSPC) did that strange thing that happens every so often with market-cap-weighted indexes. Well over half of the 505 individual stocks held in the index closed lower on Aug. 25, but the sheer size of some of the best performers resulted in the index closing up 12.4 points, or about 0.34%. 

The biggest news driving the winners today was the announcement from S&P Global yesterday that some major changes are coming to the Dow Jones Industrial Average (DJINDICES:^DJI). Effective Aug. 31, Amgen (AMGN 3.24%)Honeywell International (HON 0.37%), and (CRM -2.09%) will be joining the Dow, while ExxonMobil (XOM 2.97%)Pfizer (PFE 2.23%), and Raytheon Technologies (RTX -3.46%) are being removed. 

Blocks spelling the words chance and change.

Image source: Getty Images.

As a result, shares of Amgen gained almost 5.4%, while Salesforce and Honeywell stocks gained over 3%. On the downside, ExxonMobil lost 3%, while Pfizer and Raytheon both lost about 1.5% on the day. Other big winners include Gap Inc, up 10.4% following an analyst upgrade, and J.M. Smucker, with shares up 7% on solid earnings. 

Dow changes, mega-cap gains drive S&P higher

In addition to the market-moving announcement that the Dow Jones Industrials was swapping out three components, large-cap stocks Starbucks and Advanced Micro Devices, and mega-cap Facebook all gained more than 3% on the day. The sheer size of the best-performing stocks on the day was enough to make up for the 350-plus S&P 500 stocks that lost value. 

The changes in the Dow were precipitated by Apple's planned stock split, which will have a large impact on the index (which is weighted by stock price). Pulling out one of only two oil companies in the index -- Chevron will remain -- and replacing it with global enterprise software giant Salesforce, and replacing Pfizer with mega-biotech Amgen, will help balance out the amount of influence an individual stock's movement can have on the Dow. S&P Global also said that the move was designed to rebalance the Dow across sectors. This is where adding Salesforce comes in. 

The three companies being added have been far better investments over the past five years than the ones being removed: 

CRM Chart

CRM data by YCharts

Retail, travel stocks fall as coronavirus worries continue

Stocks that fell the most included retailers Best BuyTiffany, V.F. Corp, and Tapestry, oil refiner Phillips 66, and airlines United Airlines and American Airlines. These companies are representative of the kinds of businesses that have struggled under the weight of the coronavirus pandemic and the recession that it has caused, and stand to struggle the most if the economic overhang lasts longer than expected.

There is reason for optimism, with prospective treatments moving forward in clinical trials, and multiple vaccine candidates expected to get consideration for an emergency use authorization by this fall. Factor in what is likely to be a contentious campaign between President Donald Trump and former Vice President Joe Biden between now and November, and investors should expect plenty of volatility in the weeks and months ahead.