why do some people call some of their managers dumb in the IT industry

Today i attended a book review and topic of discussion was on leadership and management.
People in the room were trying to relate the things told in the book to some practical scenarios in IT/Technology industry.

One of the things the book was talking was about different levels of managers and the level of details and subject knowledge required at each level. So it said people at senior management level need not know subject details and most focus more on strategies.

In the same context one of the gentlemen raised a topic saying "if the manager doesn't know java, then the java developers reporting to him call him dumb. it's really wrong on the part of the developers because manager need not know it" . People were condemning this and were saying in such situations it's the java developer who is dumb and not the manager himself, because the manager need not know so much of things :)

Well, i actually agree to this to large extent that the manager need not know the details.

However why is someone being called dumb needs a different analysis.

Below is one of the common conversation between managers (the dumb one's) and subordinated

Manager: How much time will it take to develop a application which has feature X from MS Office, feature Y from the Drupal and feature Z from the Amazon e-commerce site.
Developer(hard core): it takes 6 months approx to develop.
Manager: hey come on...I thought it will not take more than 1 week. You have everything already available in MS office, Drupal and Amazon. You just need to look at them and write some java code to integrate the different features.

Developer: (whisper) Now how do i explain this guy that these are three different vendor applications without the source code.
$!^&@??? head bang bang bang...


Now wouldn't the developer call him dumb?

Many times managers do this Or rather any individual does this because he doesn't want people to take him for granted and show that he as well understands and has control of things.

It's like me going to a tailor and telling her ' i know this doesn't take more than 3 days then why are u taking a week to stitch' . Well in reality, i may really not know how much time it takes ;) , and that's just a trial and error strategy to ensure that the tailor doesn't fool me.

Similarly the problem with some of the managers who are considered dumb is that we sometimes try to interfere in areas where we are not comfortable.

And my personal opinion is that if we are in the IT industry and heading a set of technical people, then as a manager either we should have some basic knowledge of what's happening so that things don't go out of our control.
OR
we should respect and trust the words of our subordinates who knows things.

If we don't do this then obviously we would be called dumb.
Otherwise managers are the most important assets in a company:)