one of the reasons i listen to drum and bass is for the speed as i'm pretty sure most people do so i don't really see why dubstep drum & bass get linked, or even talked about at the same place
Both came about from the same scene really, its just a tempo thing. Also, alot of dnb producers/djs and dupstep producers/djs cross over.
Side point, went to a dubstep night last night (first time going to an only dubstep night) and it was fucking sick! All about the underground dubstep, much less wobble and horn and more clinky and beaty.