Keep in mind - 99% of the population wouldn't have been able to figure out how to spoof the user-agent to get into the AT&T site, and most of those that could, wouldn't have gone beyond extracting a couple IDs, and then notifying AT&T.
Weev's sin (if not felony behavior) was extracting 100,000+ personal email addresses, and the exposing them for the sheer purpose of embarrassing people he despised. Do I believe he engaged in illegal behavior? Yes. Do I believe it merits years in Jail? No.
With regards to legal obligations - In California, the closest I can find is Bus. & Prof. Code §§ 22575-22578 [1]. It is a requirement for site collecting personal information to "conspicuously post its privacy policy on its Web site"
I can't find any laws in California that require the securing of this information beyond that, though.
[1] http://www.leginfo.ca.gov/cgi-bin/displaycode?section=bpc...