I think sachinag is trying to say that consulting companies are services companies, whereas startups and silicon valley seem to revolve around product companies. The semantics of the distinction are around scalability of the business. You could also look at revenue per employee or P/E ratios as other indicators.
Personally I agree that scalability is a better metric for enterprise attractiveness than raw size. Investors agree. CSC has a P/E ratio of 5.8, whereas Microsoft's is 12.9.
The list also just feels mistaken, but that might be my misguided sense of enthusiasm for shiny companies. Fiserv is a $6B company that I had never heard of. I'd probably rather go long on Facebook or Twitter, but a savvy investor might disagree.
Google's fascinating when it comes to categorization. I think it's pretty clear that they make software. What's awesome is that they, as you say, don't monetize that s/w by selling it (like 37signals or whatever other internet company); they do so through the sale of advertising space. They're the biggest dichotomy between core competencies (software engineering) and monetization (ads) that I can think of, perhaps in history.
Actually, seems like companies with wildly disparate core competencies and monetization schemes tend to do pretty well. Or maybe it's selection bias, and the ones that do well do really well but the rest fail miserably. Either way, I'm waiting for some company to close the Google -> Nike loop by leveraging their expertise in sneakers and sportswear to sell lots of software.
Also, some locations are bogus. Accenture is incorporated in Bermuda for tax purposes, but the actual work is done in many major cities. IBM, though the headquarters are in NY, has major offices in Silicon Valley.
IBM has major offices of comparable size in Austin, Raleigh, and several international locations, as well. I would say the proportion of their Silicon Valley presence is insignificant. They're probably to big and historic to localize, in any case.
These are the largest 20 companies classified by Forbes as software companies. With the large organizations it's almost impossible to say, "they do that" since they invariably do a lot of things; any other hand-wavey sorting wouldn't have been significantly more objective.
I don't think the SEC classification is useful for the purpose of locating software companies as the SEC regulates only publicly traded US companies. They're interested only in very specific aspects of a company and they categorize accordingly.
CSC, Capgemini, TCS, Infosys, Wipro, and ACS don't sell software. They sell consulting, of which actual software coding is but a part.