I think the use of the word 'delete' should not be taken literally. I believe that Facebook for example simply archives your content for posterity (and the NSA)

I think the use of the word 'delete' should not be taken literally. I believe that Facebook for example simply archives your content for posterity (and the NSA) and then marks your photo record as 'hidden'. It then removes the actual photo from the CDN. Well, that's what I would do if I was in the business of classifying every person on the planet for advertising purposes and security/population control.