True. Half the code can be anything. Half the characters in source, half the lines (Which seem more plausible since version control systems deal with line as a unit) or half of the files or even half the binaries. I'm just clarifying based on my own clarification, which half it is.
I don't think, this is any surprising at all. I believe the statistics would remain the same, for many companies.
Much more informative that the title itself.
Touching file and changing maybe one line is not a big deal, but rewriting half of the source code base every months is.
I was there, live in this presentation, more than a year ago, at Hyderabad and got this clarification from the speaker.