I have often wondered that myself. It does seem like engineers have less angst about it because they have been trained since school to play by all the strict rules, standards, and best practices that have been drilled into them.

It's possible that software development attracts more creative, nonconformist people than engineering because there is a much higher barrier for creativity and self-direction in engineering.

Sort of, but engineering is more measurable. If you can reduce a component's defect rate, then the company will likely go with your new idea. If you can't reduce a defect rate, then you won't have any lingering feelings that your way would have been better.

Engineers also tend not to have blogs to rant about this stuff, so if they do have anguish they don't publicize it. It's all kind of a generalization though, so YMMV.

In my case, it was MUCH worse. I have a BSME and worked as a Product Engineer for 2 years at a spark plug company. I hated it so much, I worked like a dog to get into IT. (There really wasn't much of an IT program at my school when I started and computer engineering was basically mechanical engineering with a computer...sigh) Most engineering work, especially automotive, is extremely boring. I'm sure an M.E. at Nasa is considerably happier, but these types of jobs are extremely rare. Moving to IT was one the of all time best decisions of my life, but it wasn't easy to make the transition.

I know that doctors and nurses often do.

As far as I know, No. I think the reason is not beacause there are more bright people in Software (would love to think that though :)) but that they have less choices.

How often do you hear a mechanical engineer leaving work to start a new company or doing a 'Mechanical' start up and selling to for big money?.

I think when you have few options and when people you identify with are doing what you are doing, these feelings of not contributing/not doing anything else are less.