I think you keep missing the point. There's no way that there is not an American with the skillset. You're just unwilling to pay an American wage for that skill set. American wage does not necessarily equal the wage in the books, especially due to our rising costs of education and certification. If the prevailing wage is allowed to be eroded by H1B's bringing it down, corporations win. I can continue to step wages down if a job is worth 80-100K a year, and I bring in H1B's for 80K. Then the job gets reclassified as 60-80, I start paying 60, and so on and so on. The wages need to be left set strictly on a non-global scale. If Americans feels that a job is worth 100K that's where the job will stay, that way Americans can competitively ask for that wage. The people that come in an say I'll do it for 80 is exactly how wages continue to get depressed and corporations just smile a little more inside.
I wonder how many folks claiming that there are plenty of qualified Americans available have ever been hiring managers for such positions. In the real world, and in most corporations, you have limited time to secure talent for an open position or you run the risk of losing the headcount. There may well
exist an American worker with the skillset you are looking for. But they may not be applying for your job in that timeframe. Or maybe they apply, but do not hold up in the interview process. H1Bs in these cases indeed serve to supplement the applicant pool. And in this very common case, they are often chosen not because they are cheaper or will work like slaves, but because they fill the need of the company at the time, and yes, often prove to be superior to other candidates in the pool.
If H1Bs served as cheap alternatives to US candidates, you would find a sizeable discrepancy in their wages relative to that of the local population, and that is simply not the case.
Now if the question is whether the presence of H1Bs overall bring down salaries on a Macro scale, the answer is of course yes as a matter of simple supply and demand. However, looking at the big picture, that increased talent pool also makes the US the prime place for companies to set up their operations and hire from, and is a reason why US companies are more competitive in general.