I think you're being a bit dramatic about little part of one sentence.

There are many application developers out there using Rails, PHP or Django who can go years without invoking locks or semaphores due to the strengths of the APIs and frameworks they use.

As they learn and grow as developers, they will be introduced to new problems and solutions. A semaphore can be exotic, not because they've never heard of it before, but because they've not used them very much outside of that one assignment they did in CS 5 years ago.

How about instead of criticizing people's eductions, we encourage them to be mindful about what they don't know, and to learn whatever they can when they get a chance?