Have you ever seen somebody make a mistake that you swear you wouldn't make if you were in their shoes, and then, one day, you are in their shoes, and you realise after the fact that you made exactly the same mistake as them? I suspect that many IT people would make the same mistakes as their managers if they were put in their shoes. Work would pile up, and you'd soon lose any detailed view of how the project is going down in the trenches, because you're too busy with the administrative stuff.
@gr33b0 No, but I talked to a guy who's a former engineer and quite new at management, and he's made mistakes you wouldn't expect of someone who's been on the floor. Basically, becoming a manager changes you, because changing circumstances change you.