To me, the advantage of USB charging units is simplicity and convenience.

I like the USB charger design. I can carry around a single USB wall charger base and two cords to charge 3 lights and my cellphone. Before I'd have to carry around 4 different proprietary charging units. If I left my magicshine charger at home, or if I wanted to charge my AA's at work, I'd be screwed. At my work, everyone has a mini or micro USB charger. I could easily borrow theirs and charge my bike stuff. That's much better than carrying around some companys' chargers that only fit that one specific light.

Sure, a lot of people don't work around computers or need USB compatability. Even then, the nice thing is you can use one single cord to charge both your MiNewt and your HotShot (or whatever else you use).