This is also why any app that handles sensitive information (including, arguably, the photo and video galleries) on a phone should have at least the _option_ to set an in-app PIN that's required before it opens up.
Lots of folks hand their smartphone to their kids to play games and even if there's nothing sensitive on there, they might have things they don't want deleted like treasured photos and videos.
Hell, I'd be happy if iOS had a way to lock down the Springboard so my kids can't screw up my home screen every time they get their hands on a device. Does anyone else come back to find all their apps dragged into countless random folders?
At work we're required to have a PIN lock on our phones if we have our email or calendar synced to it. Majorly inconvenient to have a system-wide lock, why not just give the option to set a PIN before the email accounts can be opened?
Lots of folks hand their smartphone to their kids to play games and even if there's nothing sensitive on there, they might have things they don't want deleted like treasured photos and videos.