As you could see, Silktest is lagging behind of QTP or Selenium on all job markets, but I think I have an explanation why this is happening. There are plenty of QA Tester job postings like
Required skills - Test automation, SaaS, SQL, performance testing, Load Runner and QuickTest Professional, Silk Test, Java, Visual Basic.
Perhaps I should look for Silk not SilkTest, even it would include results for Silk Performer. Unfortunately as you can see below the change is not as big as I expected. I could explain why Selenium is so popular in Silicon Valley. As an open source project, Selenium is available for free and has been used for testing at many Silicon Valley companies like Google, Yahoo, and eBay. There are also a lot of startup companies not willing to spend money of SilkTest license or QTP license. That's why there are a lot of job postings for QA Testers with Selenium testing skills in Silicon Valley. In the same time I am still not sure why SilkTest lags behind of HP QTP on national markets. Does anyone have any ideas?