I'm not a lawyer, but my understanding is that the people named on the patent have to be the actual inventors. A lawyer explained to me that you have to be the inventor behind at least one of the claims. Of course that practice can be abused.

A way to protect your inventorship is to write down what you think you invented, and submit it in writing to your employer. I work for a F500, and we have an official process for this, with a reward. It benefits the company to get patent-able ideas documented.