That's true however wired broadband is also oversubscribed in a similar way. A single DOCSIS channel can provide 38Mbit of bandwidth and it will typically serve

That's true however wired broadband is also oversubscribed in a similar way. A single DOCSIS channel can provide 38Mbit of bandwidth and it will typically serve ~250 customers. 250 customers @ 10Mbit each would require a 2.5Gbit/sec pipe at the access layer. For DOCSIS 3, 4 channel bonding, the real amount of wire bandwidth increases to 152Mbit/sec so to offer a 50Mbit connection to 250 customers your real maximum bandwidth needs balloon to over 10Gbit/sec. Cable is a bit unique since it's also a shared medium. Throwing more wire at the problem won't really help. It's a similar proposition to building many more cell towers with more antennas and transmitters to use spectrum more efficiently. It can be done it's just insanely expensive. Based on the VZ/Google deal I think the cable industry now has an excellent argument that they should be excluded from most rules of net neutrality.