I think you entirely fail to get what was being said here - and, as a bonus, then go and get your facts entirely wrong.
The bit you quoted actually states that companies have built valid businesses on open source, and gives the backbone of the Web and other Web-based services as a good example - Apache, Mozilla, MySQL, and Red Hat were all big companies,with some having now been bought by some of the major players in the software industry.
Further, that paragraph also states that Google and Facebook have taken the technologies produced by those companies and used that as the basis of their business model - so that statement is correct.
However, Facebook takes those basic technologies and extends them, writing custom code to allow their users to do new and exciting things - they write software, therefore they are a software company.
OK, so the source code may not be available to everyone, but they make their API's available, and just as they make money from web technologies, so other companies make money by writing software that runs on Facebook.
Google not only writes custom code for their search engine, but they make a lot of code available to the public - Google Earth, Sketch Up, Buzz, Chrome, Google Talk, and many more are all freely available from Google, as are a couple of Operating Systems (Chrome OS - still in development, but there none-the-less - and Android) - I think you could safely say Google is a software company.
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