It's a huge pain to fire an employee - there're dozens of potential "wrongful termination" lawsuit hitches, and if you run into any of them, you've just cost the company more in legal bills than you'll ever save in that employee's salary. For that reason, companies usually will keep full-timers even if they aren't quite as efficient as consultants or new hires, because the costs of getting it wrong and inviting a lawsuit don't outweigh the marginal benefits. Unless the employee is grossly incompetent, in which case you both save more in lost productivity, and there's a lower chance of a successful lawsuit...
