Why is it that the occasional 10% stock dividend is not treated as a split as far as the price is concerned? Is it a way to keep a lid on the price action so as not to attract much attention?
It is treated exactly as a split. On the date of the last one, stock went from about 45 to 41, or "down" 10% to reflect that everyone had 10% more shares!
Yes, but with a 2:1 stock split, the historical stock prices also get adjusted. With the 10 % stock dividends, the historical prices remain as they were, which gives the appearance that the momentum is less than it really is.