My understanding is that it is still just HTML, but the way some people describe it, it sounds like the second coming of C.
It is the next coming of C.
The moment the portable devices became web capable - and the web back then already was where most people spent their time when computing - was when the iPhone was introduced. A full-blown non-sucking modern browser on a fully mobile pocket device that the entire world wanted. That was a first. And Steve Jobs said: No,it won't run flash or any other VM. Period.
This eventually killed Flash and pushed *everyone* in the rich client field back to Ajax, HTML and CSS. At the same time browsers became more performant, Google open sourced their acqired V8 engine and moved every thinkable app into the cloud.
And the devices doing this are so powerfull, they'd run circles around an 80ies liquid nitro cooled Supercomputer. Hence rich clients in pure open standard web technologies is where *everything* that matters in utility and end-user computing today happens. That's a simple fact. Performance be damned, we have 4-8 cores running at 1.x Ghz on even the cheapest of mobile devices. So, yeah, every advancement in the field is a big deal. Web Components, for instance, are a huge step forward. (Google for "Polymer")
And why are web based rich client apps such a big deal, you ask?
From the top of my head:
No deployment, continuous integration, port 80 is always open, no fussing with customers inhouse IT, runs on everything that runs on electricity and has a screen with zero porting. And probably then some reasons.
(Sidenote: That's why we today even have tons of SCADA equipment that runs mission-critical stuff accesible to every highschool kid who can dig up the default password.)
You got it just right: The web and HTML5 centric frontends actually are the next coming of C.