I see that there have been a lot of issues raised here will I was gone for a day.
On the legality issue, I'm sure that it varies from state to state. As I remember when I was learning to drive here in California, the vehicle code stated that you could not coast down hill in neutral gears. This was in the days of drum only brakes and very poor ones at that. It was also when overdrive units would go into neutral under 30 mph when slowing down. That is how the units were designed. This is also at a time that every few months you would read of a semi loosing it's brakes and going out of control going down the grapevine grade (between Los Angeles and Bakersfield). Cars, trucks, and brakeing systems have all greatly improved since then. I have not seen this question show up on driving tests when I have renewed my license for many years. It was not a topic of discussion in any of my now grown kids driver education and driver training clases. Although I believe as I'm sure that all of you do that it would take an absolute idiot to try to take a car or a truck down the grapevine grade today in neutral using the brakes only.
On the stalling issue. Stalling an engine at idle isn't any more likely than an engine stalling on deceleration in gear (unless you forget to depress the clutch near the end).I'll make that statement not just on driving experience, but from years of experience as a drivability and tune up technician.
On the fuel economy issue. A difference in overall fuel consumption between closed throttle deceleration coming to a stop in normal driving and allowing the engine to idle by coming to a stop in neutral is insignificant. With a fuel injected car, in theory, the fuel economy would be slightly better with closed throttle and high vacuum, and I believe that indeed it would be, but hardly enough to see a difference when it's time to fill the tank. On a carberated engine, fuel economy is in the toilet on high vacuum closed throttle as the high vacuum sucks a lot of fuel through the idle ports. Again, for nearly all street driving, you are not likely to see the difference when it is time to fill the tank.
What it really boils down to, is that depending on driving situations, it is nice to know more than one way to bring your car to a stop. Just because of smoothness of operation on city streets it makes sense to kick the trans out of gear and coast toward a stop with gentle brake assistance if needed. Other times it makes more sense to select a gear or gears and be prepared for some eventuality.
Some of you may not want to hear this, but when I won an opportunity to take ten laps in a Winston Cup car at Fontana, they instructed us when bringing the car into the pits in the final approach in the pit lane (probably still doing about 50 to 60 mph), to kick the car into neutral and stop with the brakes. So it's done at Nascar (when appropriate) where control of the car is paramount.
