Consider the payoff matrix for the employee:
Employee finds a new job, old employer fails: +5
Employee finds a new job, old employer succeeds: +5
Employee stays, old employer fails: +0
Employee stays, old employer succeeds: +6 (+10?, +20?)
I wouldn't say finding a new job is equivalent to "defecting".
A better analogy is if the employer really put together an awesome team, and he hopes to work with them again in the future. In that case, honesty is better. But that's iterated game theory rather than a single game.
If you play Prisoner's Dilemma once with a complete stranger, you could argue that the Nash equilibrium is to defect. When you play with the same people over and over again, then defectors can be punished.
Unfortunately, the modern economy is more like a group of strangers playing with each other for one game. If you defect, you can always find someone else gullible to play with next time.