1. GWT is not a Google product anymore. The website has been mainly built by Arcbees, a Canadian company member of the GWT steering committee. Google is just offering to host freely the website on its infrastructure.
2. AppEngine is used to store the pages on the database so that we can change the content of the pages without redeploying the application. It's not so complex and gives us a lot of flexibility. We use GWT and not jQuery (though we use gwtQuery) because we are GWT developpers and it makes sense to use GWT for the GWT website (we use GWT to enhance the html like we would have done if we had used jQuery...). So it's not a problem of using GWT instead of jQuery. In our case, I think the main issue that make the site available offline is that CSS hide the main content until the GWT code (or javascript code if you prefer) is loaded. That why you cannot simply crawl the website from the file system.
There are still a lot of work to do on the website (like updating the content for example) but don't expect Google engineers to do that. It's the role of the community to do it. So if you want to contribute in order to make the website more user friendly for non-connected users, fell free to contribute or wait that another people on the community has the same problem and decide to fix it.
Julien