That's an interesting point and I suppose if we broke it down and asked can you be an expert in just HTML or CSS, the answer would likely be yes. However, if that's all you knew, you'd have a hard time being hired. The message I was trying to convey is to have a web career, you need to be constantly learn new things all the time.
Excellent comment, I fully agree with what you're saying. My intent was never to suggest "throwing out" previous knowledge but to instead recognize there's always more to learn and to keep building on that. Once you stop learning, the web quickly surpasses you.
Thanks for the feedback. I do see your point as well; even though web languages and design techniques are constantly changing, our end goal is usually the same. However, I still run into too many web "experts" who think they've learned it all and, in my opinion, that's an outlook that will quickly make you obsolete on the web.
Fair enough and thanks for the comment. The point I was trying to illustrate was the pace at which technologies evolve and few are quicker than the web industry. I wholeheartedly agree that the best blacksmiths were constantly improving but it was relatively slow compared to how quickly the web changes (i.e. they didn't have new tools/materials to learn every single day).
Thanks for adding to the discussion.