That is the question posed by many readers. Dan Smith deals with that subject in the 6th edition of the Atlas (p.22). Here are the differences of income between the poorest 20% of the population and the richest 20% in selected countries according to UNDP Human Development Report 1998:

Over 20 times: Brazil, Guatemala, Guinea-Bissau, Lesotho, Panama

10 to 20 times: Chile, Colombia, Costa Rica, Ivory Coast, Dominica, Guinea, Honduras, Kenya, Malaysia, Mauritania, Mexico, Nicaragua, Nigeria, Seychelles, South Africa, Venezuela, Zambia, Zimbabwe.

5 to 10 times: Algeria, Bolivia, China, Ecuador, Ghana, Hong Kong, India, Jamaica, Jordan, Laos, Madagascar, Morocco, Niger, Singapore, Tanzania, Thailand, Tunisia, Uganda, Vietnam.

3 to 5 times: Bangladesh, Egypt, Indonesia, Nepal, Pakistan, Sri Lanka.

Inequality in the US is greater than that in Europe but it soes not reach the proportions of the level of the countries listed above.
posted by Judith