Nielsen television ratings are reported as Live+SD, meaning the reports include live viewings, as well as DVR playbacks on the same day that the show aired. Reports of television ratings from DVR playbacks alone are not yet conclusive.
It's difficult to know if viewing television shows in playback would affect cancellation, or advertising, for that matter. There is the definite possibility of loss of advertisement - people who watch shows in playback are more likely to fast forward through commercials. My feeling on this is that playbacks would not have enough of an impact to warrant a full cancellation, but they may definitely affect advertising.
As the shift in television technology continues, though, advertisers will have to find a way to modify their methods for the changing needs of the public.
