Adam Bosworth is right about the limitations in so-called "Ajax" applications, and about the limitation imposed by today's browsers.
What I don't agree with: "this is all engineering, not religion, and pragmatism should rule"
This is oversimplifying.
This can be anything we want. It can be science and it can be an art too.
Engineers alone didn't design the way text is laid out in pages, or font types, or behavioural psychology.
Engineers can design awful stuff when they don't have humans in mind.
Engineers should be forced to have a look at: www.ideo.com
Pragmatism should rule in Bosworth's team if he wants it.
I know those who want to lead and innovate with their users in mind will have the great reward of gaining mindshare and enabling for a future where awful user interfaces is a nightmare from the past.
In this regard, Firefox and Opera including SVG rendering are leading the path towards better web rendering and user interfaces.