Secure routers, almost by definition, store some kind of authentication data (passwords, network filters, routing data) to perform their job.
Edit: Unlike say, hubs or unconfigured routers, a secured router's job is to transmit information for those who have been granted access. The line is getting very fine now, but according to the court's statement, the interpretation is that it would be legal to use a secured network if you cracked the wireless password and "piggybacked" off its services (because, by analogy, Internet traffic is routed through arbitrary gateways) but would constitute hacking if you altered the router's configuration settings (e.g. added your MAC address to the router's MAC filter).
My point is the student was acquitted of hacking not because "routers are not computers" (an oversimplification) but because there was no evidence of him gaining unauthorized access to the router itself.