Autoblog has an item about how NHTSA has denied a request from the Fire Equipment Manufacturers Association (news story here). The FEMA (not to be confused with Federal Emergency Management Administration) petitioned NHTSA to require portable fire extinguishers on vehicles weighing less than 10,000lbs. Vehicles that weight more than 10,000lbs are currently required to carry fire extinguishers on-board.
They also require drivers who have commercial Drivers Licenses, since these large vehicles are busses, tractor trailers, construction machines, etc. Commercial drivers are trained, at least in the basics, of fire safety. The Michigan CDL Manual , for example, has a chapter on how to handle vehicle fires.
NHTSA was right to reject the petition. Without some way to ensure that people get fire training, requiring fire extinguishers would be wasteful at best and dangerous at worst, if people try to fight a fire they should be fleeing. This looks like an attempt to enlarge the market for fire extinguishers. What FEMA should do is to sponsor a nationwide advertising campaign, encouraging drivers to buy fire extinguishers for their cars, and to offer training on how to use them. It could be very effective, if it showed examples, like OnStar, of how a fire extinguisher carried in a vehicle saved lives or property.
I personally do carry fire extinguishers in all of my cars, along with the flares, jumper cables, etc. I have never had to use the fire extinguisher, but is a nice bit of insurance.