Using a PPP basis is more useful when assessing a nation's international and domestic market as well as the structure of its economy because PPP takes into account the relative cost of local goods, services and inflation rates of the country, rather than using international market exchange rates.

http://en.wikipedia.org/wiki/List_of_countries_by_GDP_%28PPP%29

You're trying to make it sound like its some made up number and not the standard measure of GDP that the IMF, UN and all international economic organizations use. Its what the UN uses to create their HDI index for example. The International Monetary Fund uses GDP PPP instead of GDP nominal in their policies. This isn't some conspiracy to make America look bad, its the standard way of comparing GDP across countries.

Nominal GDP completely disregards the effect of inflation, currency valuation or purchasing parity.Using nominal values allows an economy to double overnight by simply having exchange rates fluctuate, even if the economy doesn't change at all and no extra production actually occurred.