Yep, I saw this right when I got into iOS 6 cause it's one of the first things I did. Also, the iPad now has a split keyboard for Emojis, before it was just a whole keyboard.
I'm sorta surprised that Apple didn't make them an iPhone 4S-only feature. "Uh..the..processor..retina..graphics flux capacitor..uh..er..is why the iPhone 4 can't have the new emoji icons. Yeah, the processor retina graphics flux capacitor isn't good enough on the iPhone 4! Buy the new iPhone 4S!"
There seems to be some confusion, so I'll try to clear some misinformation up. All of these "new" emojis that are in iOS 6, were actually put in with previous firmware and hidden, and that's why the "new" emojis are visible for anyone on iOS 5.1 or above. Apple just "unlocked" them for use in iOS 6. To get the extra emojis on iOS 5.1, you can just download the jailbreak tweak EmojiPro in Cydia, and it will unlock the same set of emojis you'll get in iOS 6.
So that's where they came from, I wonder if that app that made them available (in the app) is still in the app store. I have them saved in my notes app.