Comcast does not operate their own video delivery infrastructure. They contract that out to Akamai. Furthermore, Comcast will happily sell non-transit, A.K.A. paid peering, to all who come. They don't (and never have) sell colocation (DC space). Presumably, Netflix is just going to buy access to the Comcast network, same as every other CDN has done.

http://www.comcast.com/dedicatedinternet/