Well my house is two doors down from a decent sized/updated shopping center, and there's a piece of land that's soon to be developed so I'm sure there's no doubt that the fiber wire runs up to the node that's right off the corner of the intersection the shopping center is on. There's one up the road a couple blocks too, but I think it's an AT&T hub.Almost all nodes are fiber equipped (according to the supervisor tech in my area mine isn't but I think he's on something - talked to him because our area is extremely over subscribed. The node is overwhelmed at night and I go from 50-65/13 to 3/13).
To put it simply: from Comcast's 'main servers' to the node is all ran on fiber. Then the 'last mile' is ran from the node to your house with copper wiring, unless of course you have a fiber provider like Google Fiber or AT&T U-Verse.
Now I just wish ALL my connected devices had speeds this quick!