"find the closest fiber plant Comcast has for the HFC node that services the general area and make them give me a L3 drop to this bridge"

You are massively underestimating the work involved here. Aside from the physical constraints of needing a POP installed for handoff to your random wireless bridge, what makes you think the author can "make them" do anything? And what makes you think that Comcast could effectively engineer a solution to support this one-off installation, when they can't even schedule a normal OSP drop?

Edit: rhetorical questions aside, I actually investigated this option for my parents' old home in the boonies. Comcast actively prohibits you from doing this, per their AUP (http://www.comcast.com/Corporate/Customers/Policies/HighSpee...): "Network and usage restrictions: ... sell the Service or otherwise make available to anyone outside the Premises the ability to use the Service (for example, through WiFi or other methods of networking), in whole or in part, directly or indirectly, with the sole exception of your use of Comcast-provided WiFi service"