Present perfect continuous and "for"

Solution 1:

Knowing happens but once -- unlike waiting, you don't stretch the process of knowing someone over an extended period. It happens at a moment of time. That is why, I suppose.

You could, on the other hand, be getting to know the person better over ten years.

Solution 2:

Many words describing senses and emotions tend not to be used in the progressive/continuous form. Although many such verbs are either so abstract as to make temporal distinction unnecessary, or relate to a single instance (as Kris points out with "know") it isn't the case with all of them.

Such verbs are called stative (or state) verbs and include: like, love, believe, have (when used to mean "to own") and taste.

There's a complete list here: http://www.perfect-english-grammar.com/stative-verbs.html

Solution 3:

It’s because know describes a state of mind rather than an action, and such verbs are rarely found with a progressive construction. They are generally verbs which describe perception, emotion and thinking.

Broadcast is not a good example, because, as Hugo has explained, it can take a progressive construction.

Solution 4:

“[Subject] has/have been [verb]ing” is a construction called the present perfect continuous.¹ It describes an ongoing or continuous action which began in the past and continued until now. As Barrie says (he calls it by another name, the progressive), this construction is typically used for actions, not states of mind.

I have been knowing her for ten years.

There is only one sense of know which describes an action, not a state of mind: the archaic (Biblical) sense “to have sexual intercourse with”.² Consequently, some of your readers will wonder if you have been having sex with her for the last ten years.

This confusion is why you should probably avoid the progressive construction in that example.

It has been broadcasting for many years.

Nothing wrong here, assuming you mean to describe the ongoing action of broadcasting. It should refer back to something which is capable of broadcasting continuously, such as a radio station.

I have been waiting for an hour.

Nothing wrong here either. This sentence describes the ongoing or continuous action of waiting.