Okay, one vendor opted to do simpler emoji, but the other two displayed faces, right? Moreover, Japanese carriers don’t have the monopoly on inventing small images expressing emotions. The "Western" world had ICQ, AIM, MSN Messenger, Yahoo Messenger, and other IMs (say, Poland’s Gadu-Gadu). And all those had emoticons: typing ":D" would turn into an image of a yellow circle with eyes and a grinning mouth.
And personally, I would prefer the colorful, lively emoji, as opposed to plain punctuation turned 90 degrees. I guess all the current emoji vendors think this way.