Investors likely felt that with a compelling new product on the market, the company should have posted more meaningful growth. The stock of highly specialized healthcare company DexCom (DXCM -1.88%) wasn't the picture of health on Friday. It lost nearly 2% of its value in that day's trading session, on the back of an earnings release that raised investor concerns about slowing sales growth. The S&P 500 index outperformed the stock, and that's not saying much, as it essentially ended the day flat over Thursd ...