Hacker News Reader

Can you elaborate on this or link a resource that explains why this is the case?

It's not the case. Firewalling works the same in v6 as it does in v4, and most people will have a firewall on their router that prevents inbound connections from the Internet by default.

There's no reason to have your services listen on a public IP in such a setup.

Only if they allow access through their firewall.