I'm no economist, but I suppose the dense parts raise the prices for the whole country.
By the way, I think European style city planning is more sustainable long term. The American urban sprawl system creates obesity and muh Constitution hyper-individualism.
By Europe, you mean Scandinavia and Germany. Because UK has a horrendously bad and aging infrastructure.
The American suburb system has been found to contribute to road-rage and lower life expectancy. If you have to drive 30 minutes around a cul-de-sac just to go to the nearest convenience store, it must be a head-ache.