All the emoji part of the Unicode standard is, when you think about it, is a way to provide all the
different "WingDings-esque fonts" a common set of names/identifiers for their little pictures†, so that something that looks like a smiley face in Android WingDings will still be something that looks like a smiley face in iOS WingDings.
(Well, that, and asserting a minimum shared base of symbols that each WingDings font is expected to have depictions for. I think that's a less important role, though; they could just as easily get away with shipping a "Unicode-official fallback emoji font" instead, that would backfill for any codepoints a particular OS's emoji font doesn't have.)
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† Identifiers for the pictures themselves, not the concepts they represent. That's an important distinction, I think: there really isn't a difference in concept between U+1F601 'GRINNING FACE WITH SMILING EYES' and U+1F638 'GRINNING CAT FACE WITH SMILING EYES'—but they're different little pictures. Effectively, they're like an icon/logotype/mark, with each font giving you a different artist's treatment on that mark.)