Apple and Microsoft have never occupied this much of the S&P 500 Index, leaving some investors worried about the gauge’s increasingly top-heavy nature. Subrat Patnaik for Bloomberg News: The world’s two most-valuable companies saw their combined weightings in the benchmark jump to a record 14% this week after strong earnings reports from Microsoft and others fueled a rally in technology stocks. “It’s concerning to have such concentration in a few names and all those companies are in the very similar tech and communication services sectors,” said Michael Landsberg, chief investment officer at Landsberg Bennett Private Wealth Management. “This concentration will drive broader market performance until it doesn’t.” According to Tejas Dessai, an analyst at Global X ETFs, the growing influence…