It depends on the point you are making.You may have missed that state sales tax in the US is readily avoidable for just about anyone who cares. Very uinlike what IU understand in your system. And for those who don't care to avoid, it's typically only about 8%. The only people who pay sales tax on a camera are those who don't care about the sales tax.
Some people use the US to UK price difference to 'prove' that Canon are fleecing UK customers (which is the most common use of this argument). In that argument, the advertised price (and the tax inherent to it) is relevant because Canon has no control over the tax applied by the local market.
If you are asking 'I would not pay 6,000USD for the camera' then tax is irrelevant because the price is what it is.