It's just to explain that people in the UK earn and spend pounds like people in the US earn and spend dollars. The extremely low value of the dollar makes using exchange-rates meaningless in terms of real-world comparisons of the price of consumer goods. In other words, if I have to work, say, 5 hours to pay for a TV in the US I would be working 5 hours in the UK to pay for the same TV.
I have worked in both the US and the UK and have family in both countries, which is why I wanted to highlight that - with exchange rates as they are - suggesting that someone take the UK price and multiply by (roughly) 2 to get the dollar price doesn't give you an accurate picture of consumer spending power.
This is also why the US is such a bargain vacation spot for people in the UK right now - it's like doubling your money. Ditto why US exports are doing really well - they're artificially cheaper and more competitive because of that.