That's just plain untrue. The problem is IIT alumnus works double time to do their marketing. The IIT entrance exams are super difficult to ensure only the most hard working of all India gets through. This inturn creates a situation where you have all that good people at one place. Its but other wise obvious they do well.
But to say the ordinary Indian doesn't do well is plain wrong. Today's India was built by ordinary guys. The IIT'ians well most of them contribute to the growth of countries like US, not India.