"I picked Ubuntu natty (released in April) as a reference, ... and am considering only the “main” repository, supposedly the core of the distribution, actually packaged by Ubuntu and not repackaged from Debian."

I'm not sure I understand Ubuntu's "main," or what's "packaged by Ubuntu and not repackaged from Debian." Does this mean the author is not counting code that appears in both Debian and Ubuntu? Because I would expect a lot of that code to be GNU, and I would expect GNU code to make up a small proportion of the Ubuntu-only code.

But that must not be what it means, right? I thought nearly all of Ubuntu's "main" was just repackaged from Debian, in which case the remainder would be a very strange sample to draw on.