Question [Q] Encryption?

I read an article today (with the not sensationalist at all headline "'Factory wipe' on Android phones left naked selfies and worse, study finds") about factory reset not completely wiping data from the phone so that it could be recovered using "forensic tools". So just like any other bog-standard file deletion that doesn't do multiple data overwites, then. Is this a surprise to anyone?

The article also stated: "Android 3.0 onwards has offered a setting which will encrypt the phone, using a cryptographic key generated from a user-provided passcode."

I couldn't find such a function on my Acro S running 6.2.B.1.96. Should it be present or did Sony deliberately leave it out?