Sector leading stocks fell across the board Friday as the major averages slumped, but volume was weak and a number of leaders found support at their 50-day lines. Apple (AAPL) held up well after jumping above 600 on Thursday for the first time since April on reports that it will introduce a smaller, cheaper iPad in the fall. The stock dipped a fraction, losing 4.06 to 605.88. By contrast, the Nasdaq fell more than 1% in volume that was slightly