Who Decides What Words Mean

Bound by rules, yet constantly changing, language might be the ultimate self-regulating system, with nobody in charge.

Listen to Lane Greene talk about the nature of language. 

Language changes all the time. It's a system in constant flux. I'm sure you've met people who abhor when someone uses or spells a word improperly. And to some extent, their concerns have merit. They are usually concerned that by misusing words, we strip them of their original meaning, and as such it threatens the order and usefulness of our languages. And yet, no language has fallen apart due to lack of care. Some how, even with all these constant changes, our languages don't devolve into chaos. There isn't a single language that has become unusable or inexpressive as a result of people's failure to uphold traditional vocabulary and grammar. 

Every language existing today is fantastically expressive. It would be a miracle, except that it is utterly commonplace, a fact shared not only by all languages but by all the humans who use them.

How can this be?