Well, Comcast has no obligation to Netflix. Nor youtube or Hulu or any other website. But it does have an obligation to its subscribers to provide access to the internet. If its customers can't access Netflix because of a deficiency in the Comcast network and its connections to the web, it should be Comcast's responsibility to remedy. This is the net neutrality argument, and has generally been the status quo.
Currently, Comcast is arguing that Netflix is the one who has to pay to fix Comcast's deficiency, and so far, Netflix has caved and is paying.