-----Original Message-----
I imagine Netflix is mature enough to track this data as you suggest, and that's why they use AWS - downtime isn't a big deal for their business unless it gets really, really bad.
There is another possibility that is probably much more widespread amongst AWS (and other cloud) customers. Here is the scenario: You are a small, hungry startup. No capital for servers. Cloud seems great. Then, big growth hits! Cloud seems even better - you may have the capital now, thanks to friendly VC/public investment/private equity, but you don't have the time to catch up. So, keep using cloud. Then, the now mid-sized company discovers one day that their use of the cloud is no longer economical, if it ever was. They are big enough to use a dedicated hardware in collocation or wholesale datacenter solution, with blended transit from some upstreams. But the cost to transition out of cloud is big, too. So, they might go with a hybrid strategy, at least for a few years. This happens all the time. Not saying Netflix is doing this, but lots of other folks are. It’s a trap that’s easy to fall into. Especially with rapid growth. - Dan