Hello Jonboy
I'm sorry but I can't subscribe to the conspiracy theory.
There are many pressures brought to bear on car manufacturers and car owners to move towards more economical cars.
If you look carefully at recent developments in cars, we have seen what seems like some quite dramatic improvements in MPG. but you need to beyond raw MPG figure to how they are actually achieving it.
Hybrid systems, that only turn the engine on when the power is needed, so in city traffic electric motors take over which means power is only used when the car is in motion and the engine is never left idling.
Reduced performance - where in Britain is the ability to accelerate to 62mph in under ten seconds necessary? Much more fuel is used during hard acceleration, so reduce the performance and fuel savings are made.
Lighter cars means less power is necessary to achieve the same performance as a heavier car.
Better aerodynamics do help at speed, Lower power delivery from engines to maintain same high speed.
In all the above Its not that engines are getting significantly more efficient, its more to do with the way the power available is used. As a result 1 litre of fuel will still produce roughly the same amount of motive power, the key is were wasting less of it.
The car industry is simply following the customers demands, and here it is important to realise there are far more cars sold that never tow than those that do, so towing ability is not top of the manufacturers 'must do' lists.
The problem is that the caravan manufactures have either not foreseen the public's wish to down size cars, or they are are unable to make any major weight savings.
As others have pointed out, it seems the average caravanner is demanding more home comforts, and these come with both weight and price compromises.