Yes. It is a double standard. People do make more money by negotiating a new job than they ever could by excelling at the one they work at.
Most of us are conditioned from the beginning not to negotiate, we can't do so until late in the game, and even then it can be difficult.
Someone who enters a job straight from school (after having been conditioned to believe that parents, teachers, authority figures generally have your best interests in mind and don't negotiate) is less likely to negotiate.
Someone who starts a minimum wage or entry-level job probably doesn't have a chance to negotiate because 800 other applicants are willing to take it for minimum wage.
Later in their career, having worked their way up but discovering that others around them make more, they may realize that they're being cheated and negotiation could be a good idea. So they apply for a new midlevel job at a different company, negotiate, and do well.
Meanwhile their new coworkers who worked their way up from a non-negotiable starting point make much less, even though they may have more company-specific or even industry-specific experience. Typical corporate policy limits raises by percentage, so they can never even reach equal pay no matter if they excel at their job.
Therefore, having been cheated, they apply for a new midlevel job, negotiate, and do well. While their new coworkers who worked their way up make much less...