There's not 64k of assembly pumping bytes into a framebuffer and twiddling the PC speaker port to synthesize digital audio.
Of course. But all the creative work is squeezed into 64K.
One thing I couldn't find in there (and I've been out of the scene for a LONG time, so I don't know how this works on new-fangled fancy computers...) -- do these write directly to the video hardware? Or do they use OS services like DirectX11, etc?
They use DirectX, because that is the only way to support a reasonable range of hardware. (Also, you can't hit the hardware without installing a new driver or exploiting a kernel bug. Neither of which is very friendly.)
But are people still getting down and counting clock cycles?
Cycle counts aren't even documented today. Now it's all about avoiding cache misses and cache invalidation.
With Intel you have to buy a CPU, buy a north/southbridge. If you want custom interfaces beyond that, that's more chips too.
Not so. Intel has SoCs now. Apparently they're quite popular for use in IVI applications.
Apple has way too much experience being burned by Motorola and IBM both being unable to supply chips in heavy demand.
As I recall, Motorola and IBM had no problem with regular supply. The problem was that Apple was the only major customer for desktop/laptop-suitable PowerPC processors, and those vendors quite reasonably expected long-term order commitments for these products while Apple wanted more flexibility. With Intel, Apple is just one of many customers and while it has less control over x86 processor development it also doesn't have to make such commitments.
There is a hoax running especially in Europe, +358 or similar number, similar to Italy code (+35). Once you get a "ring" from that line or tricked calling it, your phone bill will be doomed. I speak about thousands of dollars (euros) here and you can't get that money back.