This game is not available in the Dutch Apple App Store :(
However, now I just opened App Store, searched for "angeldust", and bought it for less than 5€... so clearly it is available.
So it has something to do with the path a user takes from the link on your website thru the Apple dialog that asks where to open the link [App Store], etc.
If you're still interested in trying out the product, can you try manually searching for "Angeldust"? I'm using the Dutch App Store(s) and the product shows up on multiple Macs and with/without being signed in.