I'm no fan of Dijkstra, at least when it comes to his views of what CS should be all about. He wanted to turn a rather boring field into something that is much worse.
The point of the analogy is that implementation -- essentially what CS is all about -- is not interesting just as the way you construct a pen or use it to write grammatical sentences is not interesting.
"The point of the analogy is that the implementation -- essentially what CS is all about..."
Computer Science is not about how to build a computer.
Computer Science is about what you can do with a computer. Google's pagerank is computer science. Recommendation systems, like Amazon and Netflix use, are computer science. Computer science is about discovering new ways to design bridges -- not about building them.
The point of the analogy is that implementation -- essentially what CS is all about -- is not interesting just as the way you construct a pen or use it to write grammatical sentences is not interesting.