I cannot speak for the entire city, but I live in the South End and get it. A friend and fellow season-ticket holder lives in the North End, and he has it too (and does not have a sports package).
Funny story, last year I tried to buy SNY before I knew that I already had it. Spent over an hour on the phone with a Comcast agent, who had no idea what it was. They did some research and called me back, indicating that they had no record of the channel. They then called back and concluded that Comcast Boston did not offer that channel. I later flipped through the channels based upon some posts on the board here and found it...and I have had it ever since. Prior to later game last season, it went off the air (in retrospect I learned that SNY blacks out any game that is offered on one of the ESPN networks), so I called Comcast again to see if it could be fixed...went through the entire conversation again. They don't even know that they are offering it to their customers. My sense is they are not paying SNY to offer it, thus they don't charge their customers. I wouldn't be surprised if the same was true of the BTN.