According to a paper titled "Silicon Valley's New Immigrant Enterpreneurs)"[1], Indian and Chinese enterpreneurs were responsible for 24% of the technology businesses started between 1980 and 1988. So the idea is definitely backed by statistical evidence.
Besides, if there are qualified Americans who can fill these jobs already, why exactly do we have a talent shortage in tech?
[...] Estimate of ethnic entrepreneurship in Silicon Valley was obtained by identifying all businesses with CEOs having Chinese and Indian surnames in a Dun & Bradstreet database of technology firms started since 1980. According to this count, close to one-quarter (24 percent) of Silicon Valley’s technology firms in 1998 had Chinese or Indian executives.
Technology company executives are salaried employees - even at C-level, they do not create tech jobs any more than the HR department. Moreover, it's a well-known fact that C-level executives rarely come from founders (example: http://management.fortune.cnn.com/2011/03/29/why-startup-fou...). Not to mention that an ethnically Indian/Chinese person is not the same as an immigrant from India/China.
If there are qualified Americans who can fill these jobs already, why exactly do we have a talent shortage in tech?
Because "we" don't pay enough? Because "we" won't look at anyone over 35? Because "we" demand a statistically improbable combination of skills plus open-source experience plus hobby projects? Because "we" equate talent with blogging? The list goes on and on.
(FWIW, I am an immigrant).
That's not to say that a free-for-all immigration policy is best for any country. Too many people moving around too quickly can be destabilizing. But it's not like there's a fixed pile of jobs and a larger pile of people, and it's like a game of musical chairs or something.
Economies are driven by demand (consumption drives production), and economic policy is really about creating circumstances in which that demand can flourish and result in economic activity.
A good analogy would be the financial systems of London and New York. Just because all the financial people congregate there doesn't mean they are taking jobs from the local talent.