With the iPhone Apple has squarely planted itself in the second category. They even promoted them as a pseudo-SDK for a time! (And maybe gave up too soon?)
Flash-free, Silverlight-less, but full of interactivity and cloud-based applications, Apple just unleashed .Mac upgrade MobileMe complete with "desktop class" mail, calendar, contacts, and photo gallery web apps.
Check out the read link for more on Apple's use of SproutCore, and how it might just be part of a growing trend for open standards-based web interactivity.