Whether they can make it economical enough to actually be worth it is another issue, however... Still, yay for a possible very slight reduction in greenhouse gas emissions, I guess?
Maybe "Grandma DS9" would argue that the answer is right there in the implied question... :P
Politics and PR are also mentioned in the movie -- Pandora is being mined by a corporation that has to worry about things like marketing, shareholders, and maybe even legal consequences for the actions it takes. Nuking a bunch of giant natives from orbit would probably make BP's oil spill look like good publicity. :P
I'd definitely love to see a number of lifestyle and behaviour changes, and a number of broad social changes, and you're right that such things can potentially change the world far more than any technology. But things like that usually evolve slowly and in a somewhat unguided way, and the most any single entity can hope to do is apply a bit of pressure here and there through, say, the media, and even that won't work as intended most of the time.
I mean... Okay, how would a company, or any other entity, go about pursuing such solutions? Would Google put up a bunch of public service ads to try and get people to drive defensively? Because I don't think that would be a very effective way of changing the world...
A technological change is something that seems much more clear-cut and easier for someone to consciously achieve.
(Not to mention that there won't be so many drunk drivers on the road to begin with -- a drunk gets into their car, "beep-boop, my integrated breathalyser detects that you are too drunk to drive, manual controls locked out, autopilot for home engaged" -- could save quite a few lives right there).
Even a limited self-driving car that had to follow, say, some sort of indicator along the road like a train on rails would benefit from having near-instant reflexes, applying the breaks in just the right way the moment something appears on the road ahead.
This is definitely something of a sci-fi-ish scenario for now, but 1) that's exactly why it's exciting that some company is working to develop the early stages of the technology today, and 2) while we've had many "where's my jetpack" -- style disappointments about the future, computer technology is the one field where technological progress has been, and seems to still be, fast and exciting, and that's exactly the field of technological progress that may eventually lead to self-driving cars.
Anyway, those are my speculations. You're right that cars are insanely expensive, but processing power, on the other hand, is always getting cheaper, so in the end, once the technology matures, it may not add that much to the cost of cars today. I think that if the technology keeps being developed, there will definitely be a day -- probably several decades in the future, but still -- when insurance companies will give significant breaks to people who are willing to let adrenaline-free, reaction-delay-free, eternally-sober computers do their driving for them, and it will be the old-fashioned and adventurous "manual" drivers who'll be shafted with increased premiums. :P
The scale Jupiter is about 11.2 times the size of the scale Earth, for example, which matches reality.