Pages are a good metaphor for many websites. Many RIAs are better suited to a single-screen metaphor (for example, my own business, Woobius, or GMail, or Google Maps), but to claim that, for example, a blog, or HN, should be single-page, is silly.
Use multi-page metaphors where it makes sense. Use single-page metaphors where it makes sense. Don't go on crusades trying to force round pegs into square holes, or vice versa.
This particular project chose to use GWT. While GWT provides a lot of good abstractions to build such application, I find the requirements for the project is disturbing: want to be like desktop, but looks like a web-app, but can do bookmarking, etc etc.
It suffers a lot of issues from:
1) Having to re-implement how the history works
2) Having data freshness issue vs not re-fetching every visit
3) Huge DOM structure within the single page
It's just too crazy. Luckily GWT ease the pain a little bit, but I wished we wouldn't go that far or at least cap the requirements with some limitations.