I noticed today on my iPhone and checked later on my iPad when I had notifications on the lock screen that you are able to slide the icon of the notification and it will unlock and launch the app related to the notification. This was not when the slider says "slide to open." I accidentally fat fingered the slider on my iPhone and noticed that I didn't get the slider but instead got the icon of one of the apps I was notified about having new information for me. I just tested it on my iPad (iOS 6.1.2) and it launched the iMessage to the person who messaged me (my wife as we were testing this).
I have no idea when this way to unlock came about. It could have been iOS 5, but I no longer have my iPad 1 to check with, I think it came with iOS 6. Anyone know?