Interesting but the absolute figures are not helpful due to the way the survey is conducted. But the macro trend over a long period is clearly up; we just don't know where is actually lies as a true %.

Valve will have far more accurate idea of actual numbers as they will be able to correct the raw survey data using other information and data they hold and collect. But they'll never release that as it's a commercial advantage to them to know so much about the PC games market.