Apple's own 7-for-1 stock split last June enabled the stock to come under consideration for the Dow.
"Apple's split brought the stock price down closer to the median price in the DJIA. The Visa split will reduce the technology weight in the DJIA and make room for Apple. Among the current DJIA constituents, AT&T has one of the lowest prices," David Blitzer, chairman of the S&P Dow Jones indices index committee, said in the press release announcing the change on March 6.
The addition of Apple to the Dow does not necessarily translate into immediate gains as new blue chips tend to underperform after joining the index.