Comment Bad examples (Score 1) 809
I'm going to echo what others are saying and say that I think your examples are bad. I wouldn't necessarily expect a developer to understand public key encryption unless they had a background of working with public key encryption. You don't necessarily need to understand that sort of thing to make web applications or iOS apps, so it really depends on the kind of development you're doing.
Regarding file encryption, I find the question to be reasonable. If you want to send an encrypted Excel file to someone, it's probably smarter to just use the built-in password protection and encryption. If you can trust that someone has Excel enough to send them an Excel file, then you can assume they have Excel enough to open a password protected file. I would not, however, trust that someone has GPG installed.
Getting back to your question, I generally estimate that roughly 80% of people are bad at their jobs, whatever they do. This is based on a couple decades of anecdotal evidence in the professional world, but it's borne out with the new experience I continue to have, and other people seem to share the experience.