Please read the fine print!
Overall, quite an informative and useful overview.
However:
"Of the licenses, GPLv2 is the most popular for open source, but arguably, it's not the most "business friendly" - meaning companies can't alter code or keep their changes or make money off of them."
Sorry, but wrong, wrong and wrong!
First: by definition, one may obtain the code for open source software, else it is hardly open, is it? And once one has it, *especially* under the GPL, there is nothing preventing one from altering it. I believe that is in fact the major reason Mr. Stallman set about creating the GPL, to ensure ones right to do so!
Next: perhaps Mr. Clarke meant that companies may not keep their changes to open source secret? They may under the GPL, so long as they don't (re)distribute the resulting software.
Lastly: the bulk of Linux -- the kernel software that makes the hardware available to the rest of the programs in the operating system -- is, IINM, under the GPL, yet Red Hat and Novell, according to this very article, make millions of dollars a year distributing and supporting the changes they make for their particular variety of Linux.
Perhaps Mr. Clarke doesn't consider millions of dollars "money" -- thus his emphasis on the (to my mind arbitrary) $1 billion/year milestone?
In closing, after nearly 30 years of professional software development, I don't understand why $1 billion/year in revenue should be the primary standard for success of a product or a way of developing software. So why the repeated references to it as a goal?
In fact, the market for open source software is the only truly free market I have ever seen, and one of the most fascinating things about it has been the rationalisation of prices as compared with the more-or-less monopolistic proprietary software.
To me the more realistic standard would be market penetration: how many companies, given the choice of roughly equivalent proprietary and open source products, opted for the open one.
A factor not considered by Mr. Clark might have shed a bit more light: the economics of commodification of software once it is open.
Anyway, nice overview otherwise!