Last I checked, high-resolution scroll reporting over USB is not based on pixels but on fractions of a detent, which is annoying to say the least. Apple probably also didn't want to translate multitouch to scroll in hardware, since scrolls are not reported the same in all contexts (e.g. applications can choose whether it locks to an axis; which axes it can lock to depends on the capabilities of the view; etc.)

> But...you can inject smooth scrolling events via Core Graphics.

Applications can choose to ignore synthetic events, IIRC. Probably not an issue for scrolling, but for instance Little Snitch can be configured to ignore synthetic inputs to its security settings.