Video game sales plunged in the world's largest markets last year, according to a new report from three groups that track the industry.

One of the big reasons for the drop is that so many people have yet to ditch PlayStation 2, a gaming system that entered the market in 2000.

That means many consumers aren't buying releases for new gaming systems such as the Wii, the Xbox 360 and the PlayStation 3.

Video game sales saw a 8 percent overall decline, to 379.3 million units sold, during the year, according to a joint report by U.S. market researcher NPD Group, U.K.-based GfK Chart-Track Ltd. and Japan's Enterbrain Inc.

Japan saw the smallest drop, at 2 percent. Game sales in the U.K., meanwhile, fell 14 percent and U.S. sales slid 7 percent. The companies did not provide dollar sales figures.

Aside from Activision Blizzard Inc.'s "Call of Duty: Modern Warfare 2," the year's best-selling game, Nintendo Co. was behind four of the top five games in 2009. These included the exercise titles "Wii Fit" and Wii Fit Plus," as well as "Wii Sports Resort" and "New Super Mario Bros." for the Wii.

Anita Frazier, industry analyst at the NPD Group, said that while video game sales declined last year, "the industry is still boasting significant volumes that were unseen before 2008."