$20 is not equivalent to $500 in India. There is a difference between exchange rate and the value of currency. $20 is certainly not equivalent to $500 there, more like $50 to $70, maybe a bit more, but certainly far less than $500.
Heck, if exchange rate was proportional to the actual value of a currency, a few million dollars will probably get you a billion Japanese Yen, in which case as soon as someone becomes a millionaire in the US, he would fly out to Japan and swap his millionaire lifestyle overnight for that of a billionaire.
If not happy being a billionaire, why not a trillionaire? You would probably need only a few million dollars to become a trillionaire in Zimbabawe.