Good point. My examples should ideally be the same scale. For 4.0, I think it's about a single point of failure that, when rectified, recovery is simple. For 6.

Good point. My examples should ideally be the same scale. For 4.0, I think it's about a single point of failure that, when rectified, recovery is simple. For 6.0, some kind of permanent and cascading problem. The difference between the server being down, and accidentally shipping an update that bricks all clients.