It's amazing how fast computers are. And it's amazing how slow we make them with layers and layers of cruft built atop more layers and layers of cruft.
The difference is that all you have to do to view this is punch a URL into a browser, on virtually any computer in any form factor, and it's on your screen instantly with absolutely zero setup. Of course there's a performance cost to this incredible convenience.
Imagine if the author had instead used, say, DirectX and C++ and only bothered compiling it for his own platform. Not only would it be nearly impossible for this to have reached the same audience so quickly, but it likely would have taken the author longer to make as well because JavaScript + D3.js are uniquely suited towards rapidly making these sorts of prototypes.
Hmm, that's not really fair. Programmer time is a major consideration.
We live in a time where a complicated, interesting visualization like this can be built in a day or two, and appear as #3 on hacker news. Less than 10 years ago it probably would have taken 10x the time, maybe more, and your iPad Air didn't exist.
Without those layers of 'cruft' putting together something like this would involve weeks of work by a team of domain experts, rather than a few hours of work by a single person in his free time.
It's amazing how fast computers are. And it's amazing how slow we make them with layers and layers of cruft built atop more layers and layers of cruft.