Please note that the numbers in bold below are medians, not averages.
United States: 48 (Mean Score: 533)
Africa: 50 (Mean Score: 451)
Middle East: 70 (Mean Score: 440)
Canada: 75 (Mean Score: 566)
Western Europe: 80 (Mean Score: 560)
Mexico, Caribbean, & Latin America: 80 (Mean Score: 517)
Eastern Europe: 90 (Mean Score: 554)
Central and South Asia: 90 (Mean Score: 574)
East and Southeast Asia: 100 (Mean Score: 578)
Interestingly, the Australia and the Pacific Islands region has the highest average GMAT score: 594, but the sample size (about 1,000 students/year) was apparently too small to be included in the "median number of total study hours" data.
Best of luck on the GMAT and beyond,
-Brian








Source: GMAC and GMAC

Source: GMAC
Source: GMAC-Brian