It depends on where are you working! Also do you think plumbers salary should be less than a doctor.. It takes more years and work experience to become a good plumber. Meanwhile to become a doctor all you need to do is.. Read some books and remember some medicine names :P. 

paid.. you mean they charge more in appearance? 

Sure they should, theyare more educated, they work longer hours (sometimes they have to sleep at work), a small mistake can cause irreverible damage to a person, in addition to the human body complexity their job also requires knowledge in several fields pedagogy, diplomacy and psychology. I am surprised this point can even be arguable in CH.

I don't mean those that have a practice but those that work in hospitals/clinics.

Not only in France, you should see what a plumber costs in nearby France 

Sorry, I meant not only Switzerland. 

BTW I remember a joke of a doctor calling a plumber for a leak, after the repart the plumber asks the doctor to pay who is totally shocked. "OMG, this is more that what I invoice to my patients." and the plumber replies "i know, Doc, I was a GP in the past". This joke says a lot about this common phenomenon.

That's hilarious. After all isn't the medical function also some form of plumbing?

One could argue that although doctors may charge less per hour, they have a steady flux of patiens whereas plumbers in addition to having to factor the travel time in, could go days without a job and so the total income may not be in their advantage.

Around here, (at least in France) all handimen are sought after, so they can keep a steady stream of income.

It probably comes down to the fact that medical expenses are regulated, whereas plumbers charge whatever the client is willing to pay.