Off the cuff, one might think there are few, if any, differences between packing a DSLR system and an HDSLR system, but once you look beyond the basics, i.e. the camera bodies, lenses and tripod (the legs, but not necessarily the head), the differences start adding up.
Wires. Sometimes, they just get in the way, especially when working on a professional video production. Snaking hundreds of feet of cable around a shooting location can make it difficult for camera operators to move around, can be incredibly messy, and sometimes wires and cables can make capturing the shot you need incredibly difficult or even impossible.