That architecture will allow inter-application communication, and offline activation, and have access to the latest and greatest features like NFC, TV and secure wallets, which is why webinos has been forced to modify a few of the W3C standards as well as append a load.
This is just what WebOS did. All WebOS applications were developed using AJAX technologies, with proprietary extensions available to those accompanied by suitable certifications. Webinos is doing much the same thing, only with EU cash and the words "open source" thrown in every now and then.
Webinos is doing some server-side stuff too, and has specified APIs for dealing with remote services as well as available-service discovery. The intention is, eventually, to create a reference implementation, but for the moment we just have reference documents for both on-device and service-side APIs (PDF, and PDF respectively, both very long and very boring) which are open for comment.
The two big issues on a project like this are how many people will bother implementing it, and how the project addresses the problem of security. Lots of companies have signed up to the webinos dream – BMW, Telefonica, Samsung, NTT and the W3C to name a few – but that's not a commitment to make kit which is webinos-compatible.
When it comes to security there's the usual permissions-based model; applications present their credentials when requesting restricted APIs, but privacy is addressed directly in the concept of application contexts which are permitted access to specific user data.
The Wholesale Application Community (WAC) is trying to do the same thing for mobile phones, but at the moment other devices (such as Smart TVs and the like) are still using proprietary extensions, so a standard platform could have some mileage (though one might argue that MHEG is already providing just that). ®