Tim forwarded your email to me. We agree with you. Our emoji characters are based on the Unicode standard, which is necessary for them to be displayed properly across many platforms. There needs to be more diversity in the emoji character set, and we have been working closely with the Unicode Consortium in an effort to update the standard.
Apple’s head of communications, Katie Cotton, responding to MTV about the lack of diversity in the iOS emoji set.

Jeff Blagdon looks at the history of Emoji for The Verge:

But with the release of iOS 5 in late 2011, they made their real international debut. As people found out how to enable the characters on their phones, little pictures of guardsmen and faces with stuck-out tongues started sprouting up all over Twitter, Instagram, and Tumblr. 

I never thought about emoji because someone insisted that I enable it on my iPhone. Now I can’t stop.