I'm from India (currently in NYC though) and if you ask me - the USD 15 (say) buys the same bread in India as USD 100 (say). Hence the USD 100 in the US and USD 15 in India.
Cost of education is less in India (and so is the quality if you ask me, but that's not the point and I'm not inclined to discuss this in detail right now). Good developers in India do exist and tend to have learned things from costlier sources BUT have not paid the cost to use them (read piracy).
So in summary, in India the over cost of things was low to begin with and less money (in USD terms) can buy more. So it's a combination of PPP conversion of money and lower cost (even if purchasing power is taken into consideration) of attaining similar skills. What also drives down rates in India is more competition (high population density) - esp. from the spagetti-coder market that operates alongside the quality coder market.
Cost of education is less in India (and so is the quality if you ask me, but that's not the point and I'm not inclined to discuss this in detail right now). Good developers in India do exist and tend to have learned things from costlier sources BUT have not paid the cost to use them (read piracy).
So in summary, in India the over cost of things was low to begin with and less money (in USD terms) can buy more. So it's a combination of PPP conversion of money and lower cost (even if purchasing power is taken into consideration) of attaining similar skills. What also drives down rates in India is more competition (high population density) - esp. from the spagetti-coder market that operates alongside the quality coder market.