Earlier quoted context omitted.
But of course those demos were very limited in scope, because the development techniques used to create them were impossible to scale up.
Forgive me if I'm being dense, but I'm not certain what that has to do with the point being made. Could you explain it in greater detail? My understanding is that there are entire classes of programs where "let's put it on a website" is not a viable method. You can write many types of apps that way, certainly, but you pretty much give up anything so much as pretending to be performance. Additionally, it prevents you…
But the difference is that HTML5 games are games, and demos from 15 years ago were demos. Writing an entire app like you write a demo is quite difficult; hand-optimized assembly takes a lot longer to write than Java. The improvement over the last 15 years is in the programming language tools and runtimes, not the graphics that the programs produce.