According to the article:
"I do have a Track my iPad (app)," Schaefer said. "But by the time I tried to use that, it showed it was offline. It didn't even show that it was at the Starbucks or the Burger King."
I'll guess that the thieves showed it to one of their buddies and someone pointed out that it could be tracked.
Or, it simply hasn't connected to a WiFi access point since then. From the article:
"I think maybe (the iPad) had gotten onto [Starbuck's] network," Schaefer said. "That's when it backed up the pictures they had taken from Burger King on the iCloud."
If it's a WiFi-only iPad, it can only report position when it is connected to a WiFi access point. Unless you have it configured to automatically connect to a "public" WiFi network, it may not do so -- unless the thief connects to one themselves. After 24 hours, the last known position is no longer available.
And even then, it only knows the location of a WiFi access point if Apple has the device ID (of the access point) in their database. Someone else's Apple device with GPS would have had to "hear" the access point and report their location at some point in the past. But, the location isn't as accurate as GPS.
On the iCloud web portal, you can request an email if the device comes online. But, I don't know if that requires the latest version of iOS.
I posted this in another reply, but I think it's worth repeating:
Even if you haven't set a device passcode, you can't turn off "Find My iPad/iPhone" without entering the password for your Apple ID. This functionality was added in iOS 7:
Similar story from UK.
BBC News - iPad thief John Jeffries caught with Cloud photo
http://www.bbc.com/news/uk-scotland-tayside-central-25653313
Thanks for all the responses to my questions. I was lucky to get my iPad back, and figure the thief was most likely a tourist (tracking showed it settled down at a downtown hotel, and it was returned to the BART lost & found within two weeks because I had remotely wiped it). In the meantime, I bought a replacement iPad also with 3G. Once returned, the original iPad went to my wife after iTunes restored all my data. Having wi-fi only would suck because of the difficulty finding free wi-fi; having 3G works everywhere especially in a moving vehicle and has saved me while using gps map services when driving in strange cities I visit.
Turning off "Find my iPad/iPhone" is a pain now, because of the forced entry of a password and receiving an email alert. There are times when one does not want to be tracked. But it's a good thing to have to deter thieves.