Except with a motorcycle, you are able to get up to the intended speed for a road. A bicycle cannot accelerate or maintain as high of a speed as a car. A motorcycle does not have either of these problems.
It's not really, because a motorcycle can out-accelerate the traffic they filter past.
Also, filtering (lane splitting, white lining, etc) is often ticketed as reckless or some peer of it (on a motorcycle). While it often doesn't have its own designation -- if you are caught, you go home with a HELL of a ticket.