How common is adultery?

In the Economist a few weeks ago there was a review of a book about different nation's notions about adultery.   According to the book the country with the highest percentage of males committing adultery is Togo (37%) and the two countries with the least adulterous males are Australia (2.5%) and Switzerland (3%).

In the study, the percentage of men are those who are married and who have cheated on their spouse in the last 12 months.   It was determined through extensive surveying and might be flawed.   

The numbers seem scary.   Take Australia, the "best" nation with only 2.5% of men committing adultery in the last 12 months.   Is it me, or does 2.5% seem alarming?   Imagine, in the very best place for fidelity in world, 1 in 40 men still cheat every year!  Really unbelievable.   I would hope it would be more like 1 in 200.   am I just naive?