said by Noah Vail:
There is no evidence that an available SSID causes any significant security risk, in and of itself. It's weak or non-existent encryption; weak or non-existent passwords that make or break a routers security.
That is quite true. However, I believe his point was that one of the default SSIDs is usually a tip off that the router was never configured away from its default and is most likely still wide open.
Most non-savvy users will just buy a wireless router in a store, plug it in and once it works they're happy.