Body language

I just came across the following quote:

It is often said that in face-to-face communications, the words we speak actually account for less than 10 percent of the meaning that we convey, while body language accounts for more than half of our message (our tone of voice supposedly communicates the rest).

Now, I've read this type of quote before and it always bothers me. Quite apart from the obviously meaningless phrase "It is often said" (whenever you read such a phrase, add the words 'by mentally retarded neo-nazi serial killers'), how exactly do you measure "10 percent of the meaning" of something?
But let's say for the sake of the argument that the statement somehow holds true. Doesn't that imply that when you talk to someone over the phone, you understand only half of what they're trying to inform you about, and that when you read, say, someone's e-mail, only ten percent of the message comes across? That is blatant nonsense.

If you only understand 10 percent of what I just said, I stand corrected.