Scott is right in that plumbing is not as cut throat as electrical. The number of plumbers is not growing at the same rate as electricians. You have to ask yourself, who trains plumbers? Answer, other plumbers ( it's all kept within the trade ). Then who trains electricians? The answer is everyone.
My friends and I left the military with a lot of training in electrical and electronics. Half the guys I knew years ago ended up as electrical contractors. We had over a year of intensive training and then four years of night school that was paid for by Uncle Sam. I can't remember a single school that I have been to that offers training in the plumbing trade. There are plenty of HVAC, electrical and electronics classes but few in plumbing. The trade was never promoted the way the others were and this has led to a shortage of plumbers in certain areas. That's why plumbers can charge more. There is not one on every corner.