I agree with you Saleem, but if you have to modify than you are spending extra cash, how much would be that saving to make spending so much worth the fuel cost saved. With the OBD available for certain cars you can set it for fuel efficiency which makes the car more sluggish but improves fuel economy. I believe the only way to save fuel without spending the extra cash is by improving your driving styles. As I have been driving for the past 22+ years and have gone through a lot of models and makes, the best way to improve you driving habits is by using an American or European car which gives you feedback on how much fuel is being used in certain driving styles and if you are cautious you can use those figures to your advantage. The Japanese makes never show these statstistics and thus you might never learn. For example in traffic most of us would speed up for a while and than brake and than speed up again, whereas to save fuel, keep your distance and drive at a constant speed. This way if the traffic is slowing up more than you anticipated you just let the gas pedal go and once the traffic is moving again step gently on the gas pedal again. It takes lot less energy to keep a moving car in motion than to start it from speed zero.
Just my 2 fils. BTW I got a Jeep Commander 5.7 Hemi V8 to give me 12.5 liters per 100 Kms all by changing my driving style and no other mods.