If, as they say, TV networks' most valuable marketing tool is their own airwaves, then why don't they make more use of that tool? The answer, in part, is that keeping the number of network promos around the same levels lets the network keep the same levels of inventory to sell to paying advertisers. Who wants to cut commercials -- really?

The DVR has been blamed for a lot, from the demise of certain TV shows with lower rating, to the hindering of TV marketers' commercial efforts. Now comes a first: The DVR has taken down an entire network.