Well, no but it is a matter of degrees. As previous examples have said, if you leave your car outside the house unlocked and someone nicks it then yes, they have committed a crime, but your insurance company won't pay you the full value of the car as you didn't take reasonable steps to secure it.

If you have a metered service and someone has leeched all your bandwidth which you didn't take steps to protect the you are still going to have to pay for that bandwidth. It doesn't make the other person any more right though.

Really wireless networks should be made so that by default they are protected and to have them unprotected requires more specialist knowledge to setup.