Are the "Ubuntu Core Apps" also intended for the desktop?
That is one goal, yes. All Ubuntu SDK apps should be as usable on a desktop as they are on a phone or tablet. Since the Core Apps are a major focus for us, and an early adopter of the SDK, you should expect to seem them incorporate the convergent designs that will be available.
As it is, you can already run them on the desktop, but their UI is tailored to touch-based input. We will be fixing that soon, so they can switch between touch and keyboard/mouse inputs.