Netflix's new exclusive political drama series "House of Cards," which stars Kevin Spacey, is the streaming video's service most-viewed series in all its market right now in terms of audience and hours of viewing, according to Chief Content Officer Ted Sarandos. But if you want to know exactly how many people have tuned in to the watch season one, Netflix isn't going to help you out. Nor is it divulging that information to show creators or actors.The reason for the secrecy is simple, Mr. Sarandos said at the AllThingsD: Dive Into Media conference on Tuesday. Netflix doesn't sell advertising...