Like your analogy! :) The bigger picture is that we're approaching an energy crisis. That's why gas is getting more expensive, and that is why there is even an interest in these cars to begin with: the message isn't to "separate front end and back end" but to appeal to people who want to save money on energy costs, i.e. gasoline. But it won't work, because gasoline is just the medium, the real beef here is energy, and it's not going to get cheaper because we need more and more of it. It's not only gasoline that's getting expensive, my gas and electric bills are ahead of inflation as well.
"Solutions" covered by the press aren't really solving the problem, they're just shifting it around. "Wow! We have an air-powered car!" - without an explanation where the energy to compress that air is going to come from...
If you assume the problem is "Where will we find energy to sustain our current consumption rate?", then you're right: air-cars aren't a solution. Such a solution might not even exist.
But if you assume the problem is "How can we relieve market pressure on our most constrained resource?", air and electric cars are a solution. The hope is that by diversifying the sources of energy used for transportation, we can continue to use oil for other purposes that we haven't found cost-effective replacements for yet -- like plastics and jet fuel.
So while the cars won't solve the energy crisis by themselves, maybe they'll buy us enough time to reach the "then a miracle occurs" discovery that does solve it. Or, failing that, maybe they'll help civilization make a slow transition to reduced consumption, rather than a sharp crash.
"Solutions" covered by the press aren't really solving the problem, they're just shifting it around. "Wow! We have an air-powered car!" - without an explanation where the energy to compress that air is going to come from...