What if aproject thatv the employer was expecting didnt materialise ,Then the employer can lat go the sponsored employee from that job offer voluntarily.
Also any job can be done with some or little qualifications. I practically have seen,especially people with high school diplomas, nursing school dropouts becoming managers of chemical engg based companies. Computer programmers with bachelors in comp science from american universities were being managed by nursing school dropouts in some companies.(all these managers were american born citizens).Even the legendary Bill gates is also presumably a law school dropout.
So technically A JOB OFFER ina company can be done by a masters guy or a bachelors guy or even by a high school dropouts off course with some training/exposure.
Like I mentioned a masters guy has more chances of filtering many/most/all applicants as that qualification added deligently with some certificate(ex. a spread sheet certification ) that is related with the job offer .
There are numerous ways of filtering the american citizens with easy certifications coupled with the masters degree in any field like engg,management ans so on.
salaries and available candidates for a job vary in the american economy as evident by the recent economic downturn. So it is the employers discretion to sponsor a guy for a gc and let him go as soon as the I-485 is approved.The employer CAN cite numerous reasons for sponsoring a guy for the gc and letting him go as soon as the I-485 is approved.
The lawyers have MASTERED the art of convincing the DOL for the Labor certifications over the years by twisting the Job offer description, requirements,salary offer and succeeding in the LC approvals.