From Ars Technica:

The ESA estimates around 120,000 are employed by the gaming industry, either directly or indirectly. The industry added $4.9 billion to US GDP (gross domestic product), and the ESA also lets us know that the industry is creating actual careers. "In 2009, the average annual compensation per employee (wages, salaries and employer contributions for pensions, insurance and government social insurance) was $89,781," the report explains.