Maybe that was true in the past, but today when you delete your data it is gone. Trust me, I wrote it myself. The law enforcement guidelines that have been circulating recently corroborate this.
I deleted a couple of pictures this morning (nothing 'nekkid' ;-) and will have a look to confirm that they are indeed "gone" (inaccessible via direct URL -- albeit the URL of a CDN).
Would you happen to have the identity or URL of a specific guideline that you could point to?
EDIT: I just checked the URL of an image I deleted about an hour and a half ago, and that image is still accessible. It is under akamaihd.net; nonetheless, it is still accessible.
Is this true for all data - account details and whatnot? I deleted (not deactivated) my account a few months ago and just assumed everything would remain somewhere in FB's system.