Exchange rates when buying online in "foreign" currencies

Could someone give me a second opinion about this, as to me, it feels like a ripoff.

Having played and enjoyed the “bejewelled 3” demo, I decided to buy it. I go to popcap’s site directly, despite the demo wanting me to do it through a portal (buy direct if you can people), and the price quoted is 19 dollars 95 cents. Seems fair, so I start the rigmarole. At the final check before payment, it converts to my local currency, which is very polite of it. It is now quoting me 14 pounds 95. Something about the figure seems to convenient, so I try out a currency conversion site. Turns out 20 bucks is less thaan 12 pounds 50.

So I’m being charged a TWENTY PERCENT markup because of the currency change?

If not, what am I being charged a 20% markup for?

Anyone and everyone, comments, opinions and justifications welcome.

is it a game made for PC and you are buying it for mac? or vice versa? Because that would explain it, there is always a conversion fee between platforms.

there is no one true exchange rate for currencies. The ‘tourist rate’ for example, is always less generous than the inter-bank rates. And depending on how much money you are changing, you can get even more different rates.
Try comparing paypals exchange rates with the ones at your local bank, for example.