Good management requires a vast amount of skill, whether that's technical or soft skills. Good managers keep you doing your work, and reduce your distractions without you even noticing.
Your statement should read, "Easily 80% of the managers I've met/worked for have been BAD". See the difference?
Fair enough on the rewording but I'd hardly call management high-skill labor akin to the examples I mentioned.
Source: former software engineer turned manager. Never had to juggle so many wildly different skills in my life.
I agree with 80% being shit though. That was my motivation to go there in the first place.
The thing is, just like CS doesn't teach people to be good developers, no amount of management training teaches people to be good managers.
Also, a good percentage of the coders are pretty shit too. The networking possibilities of the internet have allowed us to isolate ourselves from that, so good developers are usually amongst themselves, be it on places like HN, or working for companies they already know have high standards.
I bet outside of out bubble, the 80% shit applies to many other professions, including our own.
I probably shouldn't say its a low-skill or brainless job (in general... though I do often get that feeling from mangers), but I just personally never put it in the class of highly-skilled jobs.
Edit: I guess that I've always just placed it as more of a 'ladder climber' type of job than a highly skilled worker type of job. But to be totally fair that is likely due to my experiences. :)