I'm not saying that for love of Nielsen (because shows I've loved got screwed by the ratings system), but basically, TV shows have two models for monetization outside of PBS:
1: Give the shows away over the air and sell ads to pay for it.
2: Sell access to the channel at a premium and make the shows worthy of the premium.
The first covers all network TV and virtually all of basic cable - even though the cable companies pay to carry the basic cable channels. The second covers HBO, Showtime, etc. In the premium model, they might care about non-traditional ways of engaging with content. Because it increases interest and loyalty, thereby driving up demand for the channel - which either can result in a better deal for the channel or more subscribers.
But for a traditional channel, all they care about is the ads, who views them, when they are viewed, and if they are viewed. Looking up info on IMDB doesn't help them, ordering the season on DVD is a nice bonus but not essential, browsing the show website doesn't help them. TV channels sell ads, and they want to sell them to the right people at the right times. Viagra ads don't run during Bugs Bunny cartoons. Breakfast cereal ads don't run during Matlock (just to use obvious examples). Cadillac doesn't advertise on a WWE show, but Kia might. They want to know who the audience is and how big it is. DVRs don't help them that much, though they are awesome for us.
The fragmentation of the TV market and the explosion of channels makes it exponentially tougher to handle the advertiser-based market properly, but still the Nielsen data is the most useful metric that they have. It needs to be updated for the modern era for sure, but it still provides the raw data needed to sustain the ad-based model.