Is project management a real job?

You can hear regularly companies saying that project manager is not a real job. If you want to work, you need to know the techniques, the business, or both. I guess this is not very true. A good project manager can find around him the right resources, he is not obliged himself to know everything and to become an expert.

Nobody worries when the CEO of an telecom company moves to the same job in a car production company. A developper can easily change company, so can a commercial.

Why is this not true for project managers? Is the project manager the only job where expertise is requested in another subject?

I work in a bank, I am not a banker, I am a manager!