the implementaion of communication systems
I questioned the same thing in school. I think it's because many electrical engineers never have a job that uses this info at all. If you do go into it, then there's a lot of information to understand how each component works. Once you understand how all of the theoretical blocks work, you can view a circuit and "see" that a part of it is just a theoretical building block. If you were to view an entire circuit without understanding the theory, you'd get so confused that you'd just drown in info overload.

Once you understand the theory, you can look into how each block is made. For example, this is what a non-op amp analog multiplier looks like: http://www.freepatentsonline.com/7061300.html
If this was part of a full circuit, you wouldn't have a clue where to start.

Another thing to note is that there's multiple ways to realize each of these theoretical elements. Engineering is all about choice.

Note: I was going to put this as a comment, but it got too big.