I think of the way the game is being played is no different than in business.
Let's say you're in college and graduating at the end of the Fall semester. You get an offer from the company you interned at in the Summer and you accept. You have 4 months until you start the new job. During the Fall your classmates are getting offers from other companies for more money than yours. Do you start looking around and interview with other companies? The answer is likely yes.
Another scenario I can personally attest to is getting offers from multiple companies. When working with a headhunter, I interviewed at multiple tech companies. More than one company made an offer. The headhunter asked me which company I wanted to work for. He leveraged the other company to get me a higher salary at the company I wanted to work at.
So, it's business whether we like it or not.