Where on the continent? GitHub is undoubtedly doing blackbox testing internally and has multiple such monitors but that's not going to capture every customer's route to them, leading to the same problem - customers experience GitHub being down, despite monitoring saying it's mostly up. Thus the impass. Even doing whitebox testing, where you know the internals and can this place sensors intelligently, even just for ingress, you're still at the mercy of the Internet.
If a sensor that's basically in the same datacenter says you're up, but the route into the datacenter is down, then what? multiply this by the complexity of the whole site, and monitoring it all with 100% fidelity is impossible. Not that it's not worth it to try, there's a team at GitHub that works on monitoring, but beyond motivation about keeping the SLA up, as a customer, unless you notice it's down, is it really down? In a globally distributed system, downtime, except for catastrophic downtime like this, is hard to define on a whole-site basis for all customers.
