Ember seems to be far stripped down from Sproutcore - specifically, it doesn't come with any kind of existing view resources or existing widgets, which is what enables those sorts of standard UIs. I suspect this is because Ember is targeted at web apps (where visual diversity is often an application requirement), while Sproutcore is going to be more focused on mobile apps (where a standard UI toolkit is not just nice, but expected).
That's true. Ember isn't trying to provide a set of UI widgets out of the box. I'm confident that Ember-compatible UI libraries will be released in the near future.
SproutCore 1.x isn't very mobile-friendly at the moment. The original reason the SproutCore 2.0 rewrite began was to make the framework lightweight so that it'd be more suitable for use on mobile platforms.
I've started a project, Ember-Titanium, that enables native mobile app development using Ember's runtime on the Titanium Mobile platform. The project is still in it's infancy, but I've already been successful at building apps with it.
