I could regale you with how we love to show loyalty to San Francisco based start-ups or tell the tale of how I met Quantcast's VP of Marketing Communications on the first full day I had my iPhone and just thought she was pretty cool. We talked about the iPhone and the good old days of the dot.com era. I am biased for supporting the home team, and I do think Krista Thomas of Quantcast is very cool.
Realistically however, the reason we're using Quantcast data for TV networks' website traffic is because we think it's the best free data around. I don't want to go off on a rant about Internet measurement here because I ranted about that for about 7 years in a former life and I have my hands full learning about TV measurement.
In short, there's no perfect measurement system, and I like some aspects of what comScore, Nielsen and Quantcast are doing. But only the Quantcast data is freely available for anyone to go take a look at (including us). It's interesting stuff and when it comes to data presentment, I really like what Quantcast does in terms of presenting the data.
A couple of important notes about the data on these charts. Quantcast's tracking is based on the notion of web sites dropping a "Quantcast pixel" into their web page code. Quantcast is still a very new company so not everyone participates yet.
As of this writing, of the TV networks only Fox, and parts of the CBS web network are participating. For everything else, the numbers represent panel-based data only, on a panel of some two million Internet users.