It's Australian based company.
From their About Us: "Cupid Media was founded in 1999 and is based on the Gold Coast, Australia."

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And believe me if they were legal should had to say "Sorry according to .... law, what we do is legal".

But what they did? Not only they refund me the price difference that I asked for, but they issued a full refund, plus they gave me for free a 3 months Platinium membership while I had paid for just 1 month.

Why? Because they scrared that maybe I'll report them. And they knew very well that this was out of law. You can't offer the same service with different price. eg. Even if they were locating in USA. I can understand to have a A price for US customers and B for outside US. But they have one price for all the world except EU. And nobody asked them to collect Euros. eg In your site all prices are in USD. This is legal.

You are correct. They are not taxing Americans in America.

But they are imposing a tax law on the US without jurisdiction.

Did not think about that. That is a good point. Although I'm with Nick though if that is what they are doing then they should state so on the web site that there is a fee for the exchange rate.

You have no idea what you are talking about. Report them to who? Interpol? No one cares. It's not illegal in the free world.

They gave you a refund and whatnot as a gesture of good will- if this story is even true.

And of course it's completely legal to have different prices. If I have a product and 100 customers I can sell it at 100 different prices if I want to.

It's illegal as it brokes the currency exchange rates. And the report is going to European Central Bank - E.C.B.

If you're so sure about your saying put a product in your site at $10 and sell it to me at 10 Euros. Then let the rest to me and soon will see who has the right. Once again. We're talking for the exact same product, with the exact same features, sold from the exact same point (in this case a website) and the only difference is that one client is EU citizen and the other is not.

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Usally I agree with all of your post that I've read months ago, even more with your signature. But here I'll not agree. Don't confuse the discount that you're free to give to anybody you like, with the exchange rate. It's like to have in your shop products with just a price without a currency symbol and according to your clients nationallity to say "You're American, it costs $100", "You're European it costs 100 Euros", "You're English it costs GBP100".

EDITED: Just to add one small details which maybe is important. I wrote about "same product... same features" etc but I forgot the most important. "Same price". In this case the only difference is the currency symbol that's why I talked for breaking exchange rates.
In any case in some days I'll post here the official reply. I post a question to appropriate department at http://ec.europa.eu/index_en.htm and I got the follow reply:

which indeed would not be allowed, since it would be misleading and leave the customer in the dark.
As long as the price is clearly stated, I see no (legal) problem with this. Just show me the law that prohibits me from charging different prices based on nationality, or currency. Mind you, I think it's bad practice and all, and saying it's due to currency exchange would be a blatant lie - I just disagree it would be illegal as long as the client clearly sees the price he has to pay before finalizing the order, and he can make an informed decision. If you disagree with such bad business practice, you need to use the consumer's power and take your money elsewhere. You see, car manufacturers for example do it all the time - the exact same car will be on sale for vastly different prices in every country, even inside the EU, even in countries that have the common currency. That's why there's German car dealers that offer reimported cars - it can be cheaper to buy certain cars for example in Italy and have them reimported, German tax and all added, than buying them here. Same for computers or mobile phones - often vastly cheaper in the US than here in Germany.

Just look at the Subscription Manager in vBulletin. You can set different prices for, U.S. Dollars - Pounds Sterling - Euros - Australian Dollars - Canadian Dollars

The European Central Bank has no authority over me. If I want to charge $10 for people paying with US Dollars and 10 Euro for people paying with Euros it is completely legal and the EU Central Bank doesn't have any say in the matter for a US Citizen. 90% sure the same for an Australian citizen but who knows what deals the Aussies did since like Canada they still want to bow to a Queen.