This WSJ story on Rasmalai Stallion Azim Premji and his company Wipro, née Western Indian Vegetable Product, says Partition was a natural immigration sieve (thanks, Kautilya):

The Muslims who abandoned India included large numbers of the most educated and successful. Those remaining after partition have become “economically, socially, educationally… India’s most backward community,” says Mahmood Madani, a Parliament member who is secretary-general of India’s leading Muslim religious organization, Jamiat Ulema e Hind…

Illiteracy is higher among Muslims than among Dalits in the key 6-to-17 age group. Although Muslims account for more than 13% of India’s population, they make up only 1.7% of undergraduates in India’s version of the Ivy League, the seven Indian Institutes of Technology. The underrepresentation is just as severe in the nation’s bureaucratic elite: Muslims make up 3% of staff in the Indian Administrative Service and 1.8% of the diplomatic corps. [Link]

Similarly, America’s massive land border with a less developed country ensured that many Mexican immigrants were both poor and illegal. Mexico’s elite is still comfortably ensconced in Mexico City.

The West Coast image of Indians as techies and professionals is due mainly to the immigration sieve. Had India shared a land border with the U.S., immigration would be less filtered. Indian immigrants would likely be perceived the way illegal Bangladeshi immigrants are in Calcutta, as poor and unskilled. And indeed, the East Coast desi stereotype is of street vendors, cornershops and cabbies.

On a shallower front, I noticed in Bombay that the richest, sportiest and prettiest never emigrated. They were doing well here despite the socialist economy. They had no burning need. Yorkshire got mill workers. America got ambitious nerds and their children. I ran into Bombay aristocrats, jocks, models and rich kids who’d not once ridden the local, the likes of which I’ve never met among desis in America.