I'm a German, so I'll try to explain (in short) what it means when a game has to be "blocked" in Germany.

"Blocked" games aren't illegal to buy or own in Germany. It's just our weird age rating system. There's the highest rating "Ab 18", which means the game is for adults only. But then there's another thing... If the guys and girls who test the games (they really play the games to see which age rating they should have!) think that the game is dangerous for kids, they can deny to rate that game. If that happens, the government can decide to declare that game as "harmful to the youth". Then it goes onto a list of games (movies, music, books...) called "Index".

If your game is listed on the Index, you can still sell it in Germany! It's just not allowed to display anything about that game in places where minors could see it. Stores are only allowed to sell the game to adults who specifically ask for the game.

Digital stores obviously can't know how old every single website visitor is. And you can't exactly "walk in", show your ID and ask for the game. Next problem: Germany's age verification systems suck! If you'd ask your visitors to verify their age, it would be allowed to display these games on your store, because only verified adults can enter that part of the site. But the systems are so bad that no one ever cared to implement them in a store. It's easier to just block a few games. Digital stores are selling worldwide, who cares about the handful of Germans who maybe would've bought the game?

Conclusion: GOG doesn't need to block german credit cards from buying these games. GOG did everything that's required by law. You can't see the game when you're "from Germany". You can't do shit about people using a VPN.

Okay, fair enough, and I certainly knew some or most of that, because it is similar with Australia.

However, I am pretty sure that there are games that not even adults in Australia are allowed to buy, because they transgress our censorship rules ... include things like rape or pedophilia etc.

They are on the same excluded list, though certainly qualify far more.

Are you saying that is never the case in Germany?

And as far as letter of the law goes, I doubt just hiding a web page would be deemed enough, for transgressing games that are banned in AUS ... talking serious transgressions. Country as indicated on a Credit Card or PayPal, would be an effective purchase block, regardless of VPN. Hell, Amazon do that just for silly Publisher contracts.

There are several reasons why a game or movie can be "indexed" in Germany:

Calls to violence
Calls to crime
Calls to racial hatred
Self-purposed, detailed depictions of violence
Suggestion of vigilante justice
Glorification of war
Violation of human dignity
Discrimination against groups of people
Glorification of National Socialism
Glorification of drug use
Glorification of excessive alcohol consumption
Suggestion of self-harming behavior
Etc.

What real.geizterfahr left out is the distinction between "List A" and "List B" of the "Index".

The authorities can also ban media altogether.
If the Federal Center for the Protection of Children and Young People in the Media (Bundeszentrale für Kinder- und Jugendmedienschutz, BzKJ) has sighted a medium that it considers questionable, it will be indexed on List A.
This means that the film (game) or a particular version of it is on the index and may not be publicly advertised or distributed to those under 18. <-- basically what real.geizterfahr said.

If this happens, the authority must involve the public prosecutor's office.
The public prosecutor's office or a court then decides how to proceed with the medium. This can take years.

If a legal authority decides that the medium is to be upgraded from List A to List B, the medium has been confiscated by the courts.

Now it may no longer be sold or lent to anyone in Germany.
The age is irrelevant.
Distribution and screening are also prohibited.
>>>Private possession and consumption of the medium, on the other hand, are permitted.<<<
The seller is liable to prosecution, not the customer.

There is a risk of fines or imprisonment of up to one year (again: for the seller - not the buyer).

In short:
List A contains all media that are harmful to minors.

List B contains all media that are harmful to minors and, in the opinion of the sighting committee, also contain content that is relevant to criminal law.

Edit: mixed up Lists A and B

No worries, thanks for the detailed info.