Teenagers 'only use 800 different words a day'

I would attribute this result more to "substantially all corpora of human languages will exhibit a zipf distribution in word frequency" than to "kids these days."

For example, off the top of my head I know you can do about 90% of jpop songs with 200 words, and I say without fear of contradiction that Wikipedia, the Bible, the contents of the Gutenberg free library, or any other substantial corpora will also evidence a zipf distribution.

Bonus points: the zipf distribution for the King James version of the Bible and the zipf distribution for text messages would be virtually indistinguishable if you rank ordered them and then swapped n% of the words across the two lists. I think n is likely to be about 10. A fun project for after Easter if they've published their dataset anywhere...

Sorry -- natural language processing is my first love.

This isn't to say that all teenagers only use 800 different words a day. I'm sure some do, but there have to be some that only do so to communicate effectively with their peers. I know that when I was in high school, using large words really didn't get many anywhere with my classmates.

I'm reminded of this: http://en.wikipedia.org/wiki/Basic_English

Now, shall we perform similar analysis on vocabulary use by the adults currently working in all those jobs British teenagers supposedly risk not getting?

That's a good thing. If you can say the same thing using simpler, or fewer terms you should. It's not hard to make something simple seem complicated, it's hard to make something complex seem simple. Look at lisp.