Comcast, the parent company of MSNBC, saw its shares plunge this past week as the company said it expected a record drop-off of subscribers for its Xfinity cable and internet service. The selloff of shares began on Thursday when Matthew Strauss, a Comcast vice-president for Xfinity, told a Merrill Lynch media conference that the company was bracing for a dramatic loss of 100,000 to 150,000 subscribers in the third quarter of this year. Shares had closed Wednesday at over $41 a share, but Thursday’s announcement led to a 7 percent price decline -- the biggest drop in share price since...