Not really. VAT is much higher than US sales taxes, but its much less comprehensive. Theres no VAT on food, fuel oil, postage, books, magazines, public transport - pretty much all the basic commodities. As a US tourist you can claim VAT back when you leave the UK anyway.
Gas is more expensive in the UK, but its not as bad as most Americans think. For one thing, a UK gallon is 25% larger than a US gallon. British fuel tends to be higher octane and more calorific, so you get higher mpg too.