If you write code, you should know what your code is running on. You should understand some of the layers of abstraction or at least be curious about them! Even if it's not related to your job, you shouldn't take the magic underneath for granted.
I see a big correlation between programmers who take a lot of this stuff for granted with cargo cult programmers - people who tend to think of things as "if I do x, y comes out" instead of "if I do x, this will trigger y, which causes z".
I've seen a lot of things in HTTP land that I wouldn't have been able to figure out without tcpdump. The most exciting thing is that livehttpheaders doesn't always tell the whole truth. :( But also subtle things like (TCP) load balancers mungling option fields, forged reset packets (and determining from whence they may have come), weird packet corruption.
Yes, absolutely I don't expect people coming from an offline world to know the internet stuff... but who's really offline these days?
Lists like these reflect your own experience. I care more if an engineer can quickly grasp the "big ideas": Maybe they don't know about threads, but do they express disbelief that they solve a real problem, or an unwillingness to explore them? A willingness and aptitude for learning is so much more important because the state of the art is a moving target.