Your comment presupposes that advances in mathematics are more important than advances in social communication. Is Mozart less iconic because his achievements were in music?
I don't see that... he just said it wasn't a fair comparison. If it comes off like he thinks advancements in mathematics are more important that other advances, it might be because he does think so, but that's not exactly what he's saying.
It's not too hard to imagine a world without facebook, but I'd find it very hard indeed to imagine a world without Microsoft, Google, Linux, Open Source or the Art of Computer Programming.
It's almost like this is one of those trick questions: "which name does not belong in this list". Zuckerberg pops out at me immediately.
All the rest is timeless, Facebook will one day be gone again, I'm fairly sure of that.
Mr. Knuth's contributions, on the other hand, are much more fundamental. But, because of this, his name remains unknown for the general population. For us, he is a titan amongst men; for the world, he'd be an old, retired professor who cannot even figure out email.