It's actually nothing like downloading songs off the internet... Not even close.
From the article:
"The question," said Kerr, "is whether it's unauthorized access and so you have to say, 'Is an open wireless point implicitly authorizing users or not? We don't know," Kerr said. "The law prohibits unauthorized access and it's just not clear what's authorized with an open unsecured wireless."
Considering an unsecured network is literally broadcasting itself (from a technical point of view) saying, "Here I am, my name is this, come join me please," and Windows (and other devices) can automatically connect to an unsecured network without prompting... it's definitely a very gray area.