This post from Slashdot will hopefully illustrate my point a bit more clearly.
If everyone started watching '24' or 'CSI' on video iPods or streamed over the Internet — instead of on TV in their living rooms — these top-rated shows would probably go the way of 'Cop Rock.' This is because Nielsen Media Research cannot collect data about what people watch on handheld video-viewing gadgets or from PCs streaming network TV shows. While Nielsen estimates around 90% of TV viewing still happens in homes, it's this burgeoning 10% that TV networks and advertisers are desperate to delve into.
Quite obviously, if more people were watching TV from the internet then they wouldn't depend on Nielsen to tell them who was watching would they? In the slashdotter's view of the world, all that great TV that only gets watched on computers and handhelds would get canceled because the ratings would be terrible.
What they fail to realize is that networks know precisely how many people are downloading content from the internet and as the percentage of people watching that way increases they will discount the effect of Nielsen on their decision making.
The problems of today will not be the problems of tomorrow. We need to simply trust that the people of tomorrow will know how to deal with them a lot better than we do.