Ben, depends on what you mean by 'defaults' -- i.e., are these user-created or Adobe-created?
Default settings can be established by the user using per-camera defaults.
Sharpening presets can also be created by the user. You can have a portrait sharpening preset and a landscape sharpening preset, for instance. Or you can go more fine-grained than that, and organize similar to how PKS works (e.g., narrow edge, medium edge, wide edge, low res, mid-res, high-res, etc.).
The main difference is that Adobe does not currently provide a set of these defaults/presets for you in Camera Raw. There is one in Camera Raw, and two in Lightroom. The creation of a full suite of presets/defaults is left up to the user.
There is certainly already the ability to tweak to your heart's content, just by adjusting the sliders.