This actually how Quest does it. Imagine my surprise when I was setting up the router and had to call and ask what the router password was and the tech said, "Yeah, just flip it over, under the serial number is a long hexadecimal code, that's your password."
At least the password was somewhat strong. I'm not sure having it printed on the same label as the serial number is a good idea though.
To me it implies that the default password can be determined if you are able to discover the MAC address. Either the manufacturer might have it in a database that could be compromised, or the algorithms generating the MAC addresses and the pseudorandom default passwords might be reverse engineered.
