leviathant is correct. My art teacher started each beginner class with a survey that asked students to draw "a house," "an eye," "a tree," etc. He then compared the typical student's drawings with real photographs by pointing out the differences in proportions, "you couldn't even walk through this door," etc.

In general he related things back to symbol vs. reality, the way the brain falls back on abstraction and its unique symbol-vision, and then showed us how a study of proportion and negative space gave us more practical creative power than we had back in symbol-land. He would put a bunch of chairs and objects on a table, wrap it in plastic, and say, "let's all draw that. Start with the negative space." This all goes back to Dr. Betty Edwards' works. In my experience I was even better at analyzing and approaching cartoony, symbolic styles after this practice than I was before.

Edit: Getting back to your question :) I think my art teacher was annoyed by an attitude of "how cool is Bob Ross--look, he's sharing his tree technique where he uses a fan brush," kind of squandering (in his opinion) an opportunity to finally show the public how to see, an opportunity to equip them with useful mental tools for approaching any kind of art.