Is this a cultural thing I'm missing?
There is also much more history of their (easy) use on iOS than Android, which did not support them very well, if at all, until recent years.
(I'm sounding like a right grumpy old git here)
Emoji can certainly stand in for text, and I see plenty of comments and text messages that consist primarily of emoji. But just as often they will accompany text to add personality or mood the way ASCII smilies or textual kaomoji always have on bulletin boards.
Now that I think about it, you're completely write. It's been years since I've seen text-speak.
Compare the following mentioned during a code review:
Your code is crap Your code is crap :-)
The first is taken seriously, the second is more of a sarcastic joke. The meaning conveyed is even stronger when the picture is a comical and brightly coloured smiley face rather than an ascii smile.
Recently getdavidhiggins posted a link on HN to http://emoj.li/ - an Emoji only chat. So it seems to be growing in popularity/ubiquity
That's a reason it is so heavily used in Japan, where they already have a two layer input system anyway. We might also have it easier and easier in ascii based languages as autocomplete like features develop and become ubiquitous.
Some Japanese keyboards will sometimes suggest emoji during input conversion (the normal kana->kanji step), but it's a somewhat haphazard way of inputting them, and it's often easier just use the dedicated emoji input. The reason seems fairly clear to me: many emoji encode nuances that don't map easily to single words or small compounds in a way that's easy for a user to predict...
[My old non-smart phone would suggest some emoji during input conversion (e.g. if you convert "ねこ", it would suggest "🐱" and "(=^ェ^=)" as well as "猫"), but my current (Japanese) Android phone doesn't seem to do any of that at all (using the vendor Japanese keyboard); to input emoji you need to use the emoji input... :]
Anyway, the main point I'm trying to make is that the method of Japanese language input doesn't seem to adequately explain why emoji are so popular in Japan, because the support for conversion-based emoji input is haphazard even in Japan.
About the android phones, I was a bit surprised by the low quality of Japanese support. But I didn't try the ATOK keyboard nor the input available on Sony phones for instance, only the Google IME. To Apple's credit, they've been doing IME on the mac for long enough to have a very good integration of the emoji in the system dictionary.
But really, my point was not only on the colourful emoji, but more on the fact that characters like ↑,♡,◎,△ are just unusable on a daily basis on a US/european computer, but are super easily summoned on a system with an IME. And Japanese people have been using these kind of pictograms in their communication for decades, the emoji used on the phones being just an advanced kind of the same thing. I think that would be the main cultural difference regarding to emoji.
The main issue with conversion-based emoji seems to be discoverability.... Besides those reflecting basic concepts, there are tons of odd or intricate emoji that you'd never even imagine existed unless you saw them first; even once you know they exist, figuring out what input maps to them is at best a crap shoot (I've never found any way of getting the input system to tell you)....
[0] http://matsucon.net/material/dic/kao01.html [1] http://plaza.rakuten.co.jp/love2kaomoji/5007/
It may also be in part due to the complexities of asian languages. (Note that this latter part is complete conjecture)
As someone else mentioned, the two layer input systems used by these languages also make inserting an emoji pretty much the same as typing any other word.