I think this was true around kubernetes 1.2, but is no longer the case. etcd is natively HA. kube-apiserver is effectively stateless by virtue of storing state in etcd, so you can run multiple copies for HA. kube-scheduler & kube-controller-manager have control loops that assume they are the sole controller, so they use leader-election backed by etcd: for HA you run multiple copies and they fail-over automatically. kubelet & kube-proxy run per-node so the required HA behaviour is simply that they connect to a different apiserver in the event of failure (via load-balancer or DNS, as you prefer).

kube-dns is an application on k8s, so it uses scale-out and k8s services for HA, like applications do. And I agree that it is important, I don't know of any installations that don't include it.

I think the right things have been built. We do need to do a better job documenting this though!