Lots of people have mentioned over-subscription, but another consideration is that while 1gbps connection speeds may be offered, they're likely to have other speeds as well at different costs. For a lot of people, even 100kbps would be an improvement over what they have (which might be dial-up, might be satellite with 2-second ping times, or might be nothing). I myself probably wouldn't notice much difference between 5mbps and 1gbps, as long as youtube works.

This could be a big deal for the huge under-served population in rural America and in developing countries. Incumbent telcos would have to have service at least as good/cheap as SpaceX's internet service to stay in business. I hope they introduce a low-cost, relatively low bandwidth plan that's accessible to the world's poor.