I have never in my life seen a company tell a valuable (note: valuable to a company is a person that is saving or making the company money, not just someone alive and willing to work) employee to go suck it, if they made a reasonable request for more money.
Why in the world would anyone think that it is ok for everyone to "Just Make More Money" simply because they are in a group?
Clearly in any group of employees, some will be more valuable to the company, and others less valuable. This is not a slight against the less valuable employees, just a fact of life.
If you can accept that all employees are not perfectly identical in every way, then it stands to reason that the productive employees do have bargaining power. Their leverage is that they can leave. It would further stand to reason that less productive or easily replaceable (unskilled, untrained, etc.) employees would have less bargaining power, because of the fact that they can easily be replaced.
With discrimination, minimum wages, OSHA, child labor, etc. already on the law books, why are people even talking seriously about unions these days?
You example is a perfect demonstration of union mentality: As a group you want to bully an extra $20k out of a firm, for what reason? Just because you are a group and can?
You will notice that you actually being worth the extra $20k wasn't a prerequisite, only that you now have the power of a union to muscle it out of the employer.