First off, the whole reason these guys got whacked by the judge is because they did the standard script-kid thing and went onto IRC and boasted about it, and talk about how they were going to take down AT&T, and make a name for their security company ( Goatse Security, obvious play on goat sex troll )
He didn't "break in". He sent requests to a publicly-accessible web server, and AT&T sent back private information. This wasn't hacking, or even a DOS attack. AT&T is at fault here.
By that rationale, any request on a web server via the HTTP GET or POST that could escalate privilege or divulge private data should go unpunished. You realize the number of vulnerabilities accessible via a well crafted GET URL? XSS, SQL Injection, tons of stuff. Ignore the fact HTTP is even involved here. This is no different than finding a weakness at any other level of the OSI model, the fact people can easily understand HTTP GET's doesn't make them any less serious and dangerous to an attacker.
Honestly, this has been argued over the Ping of Death back in the day. I mean, your simply sending an ICMP packet via a ping command, it's not like your hacking.
In the end it's about context. Exploiting a weakness is by definition hacking. Just because the hack isn't enigmatic, doesn't mean it's not a hack. Look at Jon Draper and a plastic whistle that happened to hit 2600hz easily.
"But it's just a guy blowing a whistle into a phone, it's not hacking".
These guys crafted a specific HTTP GET request that returned private data. The key in this request was generated by them based off a known flaw in ATT's systems (using ICC-ID as a semi private key). Then they shared that data with a news organization.
Sure, those of us in the industry can shake our head at how stupid AT&T was, but at the same time most of us recognize the line these two guys crossed. It's one thing to send an e-mail to AT&T and copy a security mailing list with a simple example, it's another to write a program and automate the extraction of over 120k e-mails and then package the data and send it to Gawker, while boasting about it on IRC channels.
Auernheimer likened his actions to walking down the street and writing down the physical addresses of buildings, only to be charged with identity theft.
I could make the same argument for randomly trying passwords against accounts. "I'm just checking to see if this key happens to work in this door...."