Here's my thinking:
I'm assuming the US is the largest market, at least that's what I heard on a DVD by an Aussie marketer. If you sell to the US market then your prices are probably in line with US marketers.
If a UK marketer sells a $47.00 ebook that is sold in the US he/she would end up with less buying power than if a US marketer sold that same $47 ebook. The same with graphics, services, etc.