http://www.cougarboard.com/board/message.html?id=13030017
A couple things are required to be included in Nielsen ratings - enough subscribers/homes represented and paying Nielsen to monitor/rate their network.
When you are only at 11 million you are not likely going to bother paying Nielsen...
You also don't see ratings on there for FS2 or any regional FSN/Root/Comcast, BTN, LHN, SECNW, CBSSN, NBCSports, BYUtv, etc...
National ratings unavailable for games on SEC Network, CBS Sports Network, the Big Ten Network and the Pac-12 Network, as none are Nielsen-rated.
Bottom line - they won't usually scratch the surface of networks in 90+ million homes. Although NBCSports is close...