Agreed. The main thrust of Picken's investments in CLNE and WPRT is the conversion of heavy truck and bus diesel motors to cleaner burning, cheaper LNG/CNG.
Yeah, it works very well for busses, which generally fill up in a yard where they can keep a huge tank of CNG or LNG under very high pressures and fill the bus up probably faster than they can fill it with diesel.
With cars, you can do this sort of fill at home, but the problem is the nat gas the comes to your house is under super low pressure. So you have to have this filling system that can really crank the pressure up for you. Honda uses this system called Phill.
http://automobiles.honda.com/civic-gx/refueling.aspx
Takes 16 hours to refill the tank! No advantage over an electric car except for maybe a bit more range (and the fuel and car both are cheaper).