Pretty much any system that's capable of handling IP traffic is also capable of firewalling. Not sure what that's got to do with address rewriting though.
A system that can't track connection state, or doesn't have enough capacity to do so at line rate, can't meaningfully firewall. When the norm for home equipment is ISPs sending it out for "free", they absolutely send out the cheapest stuff they can get away with, and in the pre-smartphone era that meant "modems" that would just provide a straight PPPoA connection with no firewalling.