It's relatively trivial to outsource. It's one of those services that's easy to measure, quantify, and manage (from an outsourced perspective). There's also a bit more to it then that. The Anycast routing can be quite difficult to setup and maintain. It's virtually useless outside of a very small set of protocols (DNS being one of them), so it wouldn't make sense for Amazon to bring that kind of talent in-house for something like DNS.
the mistake was outsourcing to only one provider. it's easy enough to setup a BIND slave elsewhere that automatically transfers the zone from your primary provider.
