But the number of new jobs at Microsoft/Twitter/Amazon pale in comparison to the number of new jobs in the domestic industry as a whole.
In fact, the vast majority of foreign worker visas aren't snatched up by the tech goliaths. They're snapped up by low-tier consulting companies. [1]
Google may be forced to look abroad to find rock star programmers, but the overwhelming majority of foreign workers brought in to the country are not rock star programmers. They're rather low paid consultants.
1: http://www.npr.org/blogs/alltechconsidered/2013/04/03/176134...
At the end of the day it's much easier to import top talent to fill the gap than to cultivate more of it in the U.S. Some companies like HackerSchool are popping up to address this need, but there's a long way to go.