If you have easy H-1B transfers (which we do), then this is not an issue since the H-1B worker would have no motivation to stick on in a lower wage job.
You are assuming this worker is hireable by other companies. Most of the body shops train people in a very specific and often obscure technology and they cannot work as general software engineers. e.g. my cousin was trained in COBOL and while he was smart enough to develop other skills, most of his co-workers did not. They are tied to the job. Many are even grateful simply for the opportunity to 'come to America'.
Well, if a company is willing to pay top dollar for a year to hire a candidate for a specific skill, I'd say that the specific skill should be in high demand. So it would be easy enough to find another employer in need of that skill.
what abt TCS working around this with paying high salary for the first year and then lowering the wage following year.