By Rodrigo Campos and Chuck Mikolajczak NEW YORK (Reuters) - It may be by far the most valuable American company but Apple Inc still can’t get into at least one exclusive club – the 30-member Dow Jones Industrial Average. It is, though, hurting those who tie their investments to the performance of the venerable Dow, which was first calculated in 1896 and is still probably the best-known stock index in the world. Since Apple split its shares seven-for-one last June 6, it’s delivered investors a gain of more than 43 percent including dividend payments, and that has contributed almost one third of the Nasdaq 100’s return of 18.6 percent, according to ETF.com. By comparison, the Dow’s total return has been only 8.97 percent over that period, and it has also underperformed the S&P500 – which does include Apple – and has a 9.56 percent return. Had Apple been substituted for 29 of the 30 Dow components last June, the index would have been higher.