How exactly does a hardware based router help? Is the idea that TOR is running on separate hardware, and despite the local system being compromised, the attacker can't "phone out" to find the real IP address?
It's possible to virtualize Tor (without running a dedicated router) so that it, too, doesn't know the external IP address. You can do this, as an example, in FreeBSD jails, and instruct the firewall to NAT all connections from/to the jail in which Tor is running. Of course, having a dedicated hardware router running Tor is even safer.