You've hit the nail on the head there without knowing I think Ron. As usual John posts more political crap without any real observation as to the reasoning.
The whole point of this is not to earn huge revenue, although that is obviously a by-product, it is actually intended as you suggest to move people to a more tax friendly place be that either by reducing their car use, their size of car, or their location. If you had ever had to drive in the centre of London you would understand why these sort of measures are needed. Recently at 9pm on a friday night (way after the rush hour work traffic had gone) it took me nearly 3 hours to go 20 miles in central London thru nothing other than shear weight of traffic. You will also find that most 4x4's used in central London every day are used needlessly by parents taking and picking up children from school when it would be far healthier and probably safer on Londons roads if they walked half a mile instead of reaching for the range rover keys!
What should also be considered is that most salaries in London are weighted on average around 15% to 20% over and above the salary paid for the same job elsewhere in the UK.
Hope this gives you more background info on why the problem is there in the first place and why such a taxation may be the only way forward