Upon reflection, I think my attitude was wrong. I really oughtn't to have been surprised. There were many developers in the crowd who may not have had a computer science education (developers today, especially web developers, often come from a multitude of disciplines). Sure, there were a ton of CS people, but were also a ton of non-CS people (Math, EE, psych, design, etc.). If the latter group managed to learn something new and interesting from the talk, I ought to be happy for them.
I think my reaction was a knee-jerk reaction against how easily people become impressed by things these days. It's ok to be encouraging towards others but in an atmosphere of overly-positive attitudes (especially in SV), there is a certain lack of discernment with respect to ideas and technologies which leads to bandwagonning and susceptibility to marketing (case in point, the early adopters of MongoDB). I'm convinced this has a cost to the tech community.
But that is no excuse for me to have a holier-than-thou attitude. It's condescending and discouraging toward people who are just trying to learn [1]. I retract my words.
It was a required course in my BSCS program, and I didn't even go to a big name tech school. So, yes, I'd expect someone with a CS degree to have written a simple compiler.
So really, you're surprised that not many people have taken an intro to compilers course?