rowan: From my perspective it's just about etiquette.
As I said before, all the team would have to do is replace the image price tags with actual text in an element flagged with a "price" class. If this was done consistently throughout the site users would be able to write their own greasemonkey scripts to translate the prices to whatever currency is desired.
And you wouldn't get that $5.95 = £5.99 problem :)
I understand where you are coming from, and I highly recommend you do contact support with your query. But I liken it to, if there isn't an over whelming need, then it could be put off until later. They are in beta right now, and working on what current features that have been hinted as coming, are probably consuming their resources right now.
They've admitted to working on the EULA and adding a related disclaimer before buying the title, they've admitted to adding a notice saying that peoples banks may charge fees for buying out of country, also they're working on the broken reputation system (probably going to put in a block so I don't get anymore, hahaha), as well as the PM option and updating the GOG.com downloader. The site is very much beta right now, at least the installers work, but best of luck to you if you're actually trying to download it (many people here are over in Iraq using military connections to try to get the files, and it just won't take!).
So, I can imagine they would get to it eventually, if it seemed like it was a feature they actually care for, regardless of ease, but without clarification from GOG.com we can't really tell, and again, the absolute best way to ask for a feature from GOG.com is to SUBMIT A SUPPORT TICKET! (please pardon the caps, I just wanted to emphasize this for ALL readers). Because, as I mentioned earlier as the GOG.com team loves reading the forums, they haven't always got the time.
EDIT:
I really think it'd be kind of neat if the GOG.com downloader also sort of worked like a torrent so I could seed my existing copies of games to people who have purchased the title themselves. Perhaps this would create a better connection speed for others? Not sure, anyway, it's a red herring at best.