It depends on what you're looking for. If you're doing hobbyist stuff, using Arduino libraries (or even Linux single-board computers) will get you a processor agnostic solution. However, if you're dealing with production in volume, using 95% of the capabilities of a 45 cent chip is much better than using 50% of the capabilities of a 2 dollar chip, and there's nothing that'll get you there besides dealing with hardware specific features (and therefore datasheets).

The problem is that processor agnostic platforms have to follow the lowest common denominator. An agnostic USB library which works on both USB2.0 and USB1.1 microcontrollers is going to be limited to USB1.1 features.