I don't know. Managing takes as much skill as anything I have done in my career, but there is no good way of learning it than on the job IMHO. Not saying all managers are well skilled, but saying it is a low skill job is to me grossly misleading.
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. :)