The transformation is all but complete. Ten years ago, for a given network's broadcast there were a certain number of viewers watching at any one time. Some were watching intentionally and for some it was just channel surfing. In some cases a show might be replayed again later and get a small second wave of viewers.
Now think about the huge change going on not just in the technology at work but in the social element and the reduction of randomness. A piece comes on somewhere in the world like Susan Boyle in this Britain's Got Talent from last Saturday, gets posted to youtube in various forms and has five million hits in three days. A posting of the same show's Paul Potts video from two years ago has over 43 million views. Most of the new viewers didn't watch the original airing, and almost all are watching it intentionally.
The link for a viral video gets sent to you (like it was to me), someone e-mails it, finds it in a Google search, or sees it in a school, club meeting or a church (i.e. the Jason McElwain basketball video). I probably wouldn't have come across Penn Jillette's videoblog about sincerity in your beliefs and being a "good man" if someone hadn't pointed me to it. The pointers, blogs, twitter, facebook, social bookmarks are ubiquitous (and they're all over the place too), and they have all but replaced cold-callers in qualifying an audience.
Whether it's the design of your car, the news you watch/read, or your presentation next week, there's a lot more intentionality involved - and expected in the details. "Leave nothing to chance" has taken on a new meaning. You get to choose, and with freedom comes... yes, responsibility.
Adapt, or be ignored.
Your audience expects it.