In theory we agree. But in practice there is little to no firewalling in the default configuration of home routers BUT there is masquerading NAT which behave as a firewall of sorts. NAT under linux is actually done with iptables which is considered to be an "interface to the linux firewall", although it's only for practical reason, once again.

Now I do agree that my point was kind of moot because it's indeed easy to firewall without NAT. I am all for IPv6 if it's done well. I especially like the idea of finally moving away from ARP Spoofing attacks thanks to Neighbor Discovery (ND).