Wobbles303: You shouldn't need to look up the exchange rate, the site should be doing it for you.
No, they shouldn't. Their products sell in dollars, not in pounds, and they have no way of knowing how much it would cost you as every credit card charges a different exchange rate.
You're looking at it the wrong way anyway. If you shop almost anywhere else for digital downloads, including Steam, GamersGate etc. they charge in dollars for Americans and THE SAME but in pounds for Brits.
So, for instance, whereas an American would pay $10 for a game, a Brit would pay 10 pounds, which is the equivalent of around $15.54, so a Brit on Steam or GamersGate is being charged $5.54 more for the same game an American is getting for cheaper.
GOG charges the same price for everyone -- much more beneficial for the customer. And, in fact, on almost every site that gives you the price 'in pounds', they're actually making money on the exchange rate, so you, in effect, are being cheated.