Well, every resource is locally on some physical machine somewhere. I think his point is that Github is often treated by its users as a "local" resource, in that it takes the place of what would otherwise be a local server running a Git front end or repository.
Now, Github probably wouldn't encourage total reliance on their service. Git is fundamentally distributed, so this doesn't have to be a problem. Still, the Github service is an integral part of many developers' workflow, and I do agree with the above commenter that I'm not sold on the idea of trusting remote servers with integral steps in my workflow.
For open-projects, it's a FANTASTIC platform... no doubt about it.
For a corporate closed project, I honestly would not use github - not because of any feature or lack of them, but because it's a hosted service. I want control over where my code sits, period - if only for the same reason as most hosted services - a subpoena or similar court order can be served against the provider with no notification to the owner of the data. This is the #1 reason one should be careful basing one's business on hosted services.
Now, Github probably wouldn't encourage total reliance on their service. Git is fundamentally distributed, so this doesn't have to be a problem. Still, the Github service is an integral part of many developers' workflow, and I do agree with the above commenter that I'm not sold on the idea of trusting remote servers with integral steps in my workflow.