Interesting. I'm also on iOS 6 and both show up for me. I wonder why.
Edit: in safari, the symbol shows correctly in the window header, but not the page itself. In news:yc, a hacker news app, the symbol shows up fine. It also shows up in the WebView in news:yc.
I haven't looked at the Supplementary Multilingual Plane: Miscellaneous Symbols And Pictographs [1F300...1F5FF] in a while. My favorite characters are 👹 (Japanese Ogre)👺(Japanese Goblin)👻(Ghost) and 👽(Extra Terrestrial).
The symbol 💣 (Bomb, 1F4A3) is useful for reviewing movies using Leonard Maltin's notation.
My IE10 octopus is missing 3 arms and a mouth, resulting in something that looks more like a 3-legged grey alien trying to surrender than an octopus who is smiling.
The unicode consortium is currently only adding the SMILING OCTOPUS: http://codepoints.net/U+1F419
Probably not supported by your browser's font just yet: 🐙🐙🐙