Easily forgotten, a lot of today's demos' complexity lies behind API calls to graphics drivers and OS system calls, whose implementations don't count to the byte limit.
Gosh, some guys are so easily hurt by a fact. And what "subtext" you read in my comment. Terrible. As a matter of fact, demo producers are offered more and more API choices. Compare what you had to accomplish with tinkering around with bare-metal BIOS interrupts in the 90s, compared to a full-fledged DirectX API including GPU-raytraycing almost out-of-the-box.
The ray tracing going on in this demo has nothing to do with the APIs he is using; indeed, that demo could be implemented, pixel perfect, on any platform with floating point arithmetic. it just uses the 'advanced api' to display the resulting image on the screen...
now, the point you make is still a valid one, in that we have more api's than before, but this demo is not an example of using such apis. Better 'grey area 4k' examples that would support your point, are the ones that (for example), loaded the general midi file from windows, and used it as a source of samples (that was a trend a few years ago); or the ones that make use of D3DX's truetype font->extruded mesh routine, to create almost all their geometry out of extruded Arial letters. In both cases, these are such ingenious hacks that despite being in the 'grey area', and definitely (ab)using data available in the host OS, they represent such crazed creativity you can't help but admire them.
either way, such tricks were not used here; you're just seeing the result of a very large number of multiply-add instructions, artfully composed; and that's nothing to do with 'demo producers making more and more API choices'