It's increasingly difficult to build a solid foundation for a modern progressively enhanced web app in pure HTML/CSS. It's still perfectly doable, but difficult enough that a lot of developers simply don't want do it, justifying it by saying they save a lot of time. (Usually that's short-term savings and long-term losses, but I don't want to debate that right now.) PushState does not address this critical issue.
To put it in a different way, current web standards encourage people to abandon page model entirely. When they need SEO, the thought is "oh, damn, I need to re-implement my wonderful JavaScript on the stupid server". That is backwards and is not progressive enhancement.
What we really need is an update to core standards (not JavaScript) that allows for building dynamic applications in declarative way and without abandoning the page model. Such updates are possible.
To put it in a different way, current web standards encourage people to abandon page model entirely. When they need SEO, the thought is "oh, damn, I need to re-implement my wonderful JavaScript on the stupid server". That is backwards and is not progressive enhancement.
What we really need is an update to core standards (not JavaScript) that allows for building dynamic applications in declarative way and without abandoning the page model. Such updates are possible.