Doesn't this underscore the argument against the OP? If Feymnan is correct, this means that many CS teachers don't really understand these concepts that they tell their students to be "tricky."
So, if numerous professionals are having trouble understanding a concept - or, they believe they understand something when they really don't, which is actually worse - then that seems to me to be empirical evidence arguing that said concept is probably difficult.
And of course you can make the argument that it just happens to be the case that these concepts are easy and society has just happened to promote a bunch of morons into professional positions, but I think that is the more difficult hypothesis to prove.
Feynman is wrong. Understanding something (technical skill) doesn't automatically make you good at explaining it (communication skill). Being poor at explaining something does not necessarily betray incomplete understanding.
Feynman is not wrong. Technical skill does not equal understanding something. Consider an idiot savant who is technically proficient at playing piano but can't string two words together.
These definitions of 'understand' may help:
1. Perceive the intended meaning of (words, a language, or speaker): "he could usually make himself understood"; "she understood what he was saying".
2. Perceive the significance, explanation, or cause of (something): "she didn't really understand the situation".
http://www.google.com/search?aq=f&q=define%3Aunderstand
Or perhaps these people just repeat "this is tricky" because that's what they were told. These people probably also say that Java is slow and Perl is a write-only language. It's easier than having a real opinion.
Feynman said it in reference to top-flight physicists explaining their research. I can certainly believe that CS teachers would know the words well enough to recite them to their students without having a true understanding of what they were saying.
As to why they don't understand - well, who taught them?
As the great teacher, Richard Feynman puts it: "if you can't explain something to a first year student, then you haven't really understood it"