When supply goes up price goes down. Logic 101 says that H1-B immigrants lower "the local market salary".
Another thing that would lower salaries is the movement of the jobs themselves. If companies can't get enough workers here, at affordable salaries, they'll just move to a country that likes immigration, like Canada. In fact, this has already started: http://www.businessweek.com/articles/2014-05-22/vancouver-we...
Limiting the number of new graduates is exactly what doctors and engineers have done to keep their wages high.
Only a fool would destroy his own livelihood. VCs would never, ever support a policy that would threaten their oligopoly on the good deals, for example.
Don't be a sucker. No one is looking out for tech workers but ourselves.
P.S. If these companies can successfully relocate to Vancouver it totally torpedoes the VC-sponsored idea that San Francisco is somehow essential. Limiting all the jobs to one city is NOT good for tech workers. Silicon Valley is not a good place to make money because the cost of living is stupid. I would go so far to say that the Silicon Valley anti-density and anti-development culture and government make Silicon Valley a shit place to start a company, and companies should be moving.
I would rather work in Vancouver or San Diego or most any other urban center than get raped by rent-seeking landowners in SV.
The above is not true for exceptional talent (Linus Torvalds, John Carmack, etc). I will vote in heartbeat for visas for people with total comp >$300k. If you are truly that valuable, you should be paid more than average Sr. Software Engineer at Google.