They want to include locals which means negotiating at the local level, with local affiliates, rather than the national networks (ABC, NBC, CBS). Also, the slow role out allows them to build the capacity and "pilot" the service as it grows. Necessary with the promise of so much cloud DVRing.

One thing to note, Youtube still isn't as accessible on set top boxes like AppleTV, Roku, etc. It needs to be streamed to your TV from a phone, tablet, or computer using Airplay or other casting technologies.