I searched for the post where it said that Macs are double the price in the UK. That may be the reason why they are not as popular as the US.
When I find the post, I will add here.
I think you may be right; I did a few comparisons between prices for example models (lowest end for each model, for simplicity) on the U.K. and U.S. Apple stores online and used XE.com's currency converter for currency rates. I found the following:
13" white MacBook 2.0GHz = £699 in U.K. store, $1099 in U.S. store; £699≈$1,380;
15" MacBook Pro 2.16GHz = £1,349 U.K., $1,999 U.S. (£1,099≈$2,170);
1.66GHz 'Combo Drive' Mac mini = £399 U.K., $599 U.S. (£399≈$790);
1.83GHz 17" iMac = £679 U.K., $999 U.S. (£679≈$1340);
'Suggested Configuration' Mac Pro = £1699 U.K., $2,499 U.S. (£1699≈$3370).
As you can see, the actual percentage difference in price varies between model. Still, it is obvious us Brits are getting a kind of bad deal, although I have to admit this hasn't put me off buying a MacBook. Even if it is preferable to Microsoft, Apple is still a business with responsibility to their shareholders. That's life, as they say.