In the Netherlands, "coffee shops" are more or less allowed to sell weed, but they are absolutely not allowed to buy it. Weirdness is everywhere in the Dutch weed regulations.

Buy it at all? Do they have to grow their own?

No, that's also illegal and prosecuted. It has to appear magically behind their counter in quite small amounts, or else.

Does this extend to most prohibited items, or just weed? "I don't know how it got here, but I have a rocket launcher I found just lying around."

No, it's only weed that has this "tolerated" status, where personal use and sales to individuals by coffee shops are not prosecuted (but everything else still is).

As far as I know in the Netherlands drug use in never prosecuted (maybe possession and buying), I remember they made a point that if you are in need of medical assistance due to drugs use you cannot be arrested just for that.

Some might find it weird that cannabis was ever illegal anywhere in the first place.

While I agree with the sentiment feel the urge to note that where I live but you will face punishment for having blackberries growing on your property similar to what you would for selling marijuana.

Blackberries are a national pest, and yet sell for $80/kg in supermarkets. The average person could collect over $50 worth from the side of the road in under an hour.

Australia is not known for its efficiency nor logic.

Strange for a country where you can legally smoke (and buy?) weed at every other corner.

Not legal, merely “tolerated” (gedogen) by the state and their agents.

I guess a Dutch guy living in a city, where weed "coffee shops" have been legal for decades now, might find it a bit illogical -- which it is.

It is illogical, but allows policing when things are perceived to "get out of hand" which is an interesting way to have things both ways (both as citizens, and as law enforcement). It's a delicate balance that could be easily thrown-over, but so far has managed to last. We'll see how long it can continue though given a lot of boundary-testing.