Stealing someone else's internet connection is NOT wardriving.
Wardriving is just mapping wireless access points.
Those cachers who used someone's internet connection did something illegal. (breaking into their victims network)
Depending on what kind of connection the AP owner has (dialup, paying per traffic?) it might cost his money.
Most wardrivers are against illegal use of open networks.
Which doesn't mean that everybody not securing their network doesn't deserve some kind of reminder how stupid he is ;p