What is it with crap analogies?
It isn't a car. It isn't a house. It's a router. Lots of routers in fact. That were left in public mode. The public used them. This is not difficult to understand.
You want another crap analogy? You just bought a bus, stuck "10A Liverpool" on the front of it, painted it up in Arriva's livery, stopped at the bus stop, opened the door, shouted "don't worry everyone, it's free today", and now you're acting all surprised that you got a boatload of passengers expecting to find themselves in Liverpool City Centre via Rainhill.
Unencrypted routers are public routers. Get that through your skull, and encrypt yours if you don't like that. It's not hard. As for exploits, that's a different kettle o' fish, and quite clearly a case of trespass if you've done anything more than ping the thing and ask for its capabilities (which is, duh, just what Google did). Encrypted routers are private routers.
Why the hell do idiots make things so much harder than they need to be? And why are so many supposedly smart people acting like complete fuckwits over this? Kick Google because it's Google? Yeah, real smart move, that.