Even though a fraction of the top talent leaves, there are a lot of very intelligent and talented people in India who don't leave the country.
The biggest thing that's holding back development in India is the one thing which Indians are very proud of: culture. In a country where you have to respect people purely based on age and status, bad ideas will continue to win.
http://www.wolframalpha.com/input/?i=us+population+%2B+europ...
They don't lack people who can make a difference, they lack the proper environment to make a difference. You can take all the best and the brightest of the world to india and it would not make _much_ difference unless the government initiates the right environment for change.
The graph is especially interesting.
The change has to come within.
However, the country was wasting those resources anyway.