The guy says roughly

>The question I'm asking is why does a 10 year old computer basically run current software OK while that wasn't true in the past.

I've got a theory that it's a bit related to human brain IO limits. There's only so much text, sound and video we can take in, video being the highest bandwidth and computers got to a stage where they could do video OK a decade of so ago. So increasing the output dramatically does not have a huge effect on user experience. I mean 4k video is nice but it's a similar experience to 360p.