I think the higher interest rate on your deposit on the DKB Credit card has two reasons:
+ Especially for lower amounts or money only held on the account for some days the bank wants to save the costs of the workflow for the opening of a new savings account or the account for call money.

+ According to its legal status, belonging to the local savings banks (Sparkassen) group the bank couldnīt open any branch besides the head office without harming the other local savings banks.

The Sparkassen are owned by the cities and municipalities and therefore they are also under what you would call political influence and therefore one subsidiary is not very welcome when operating within the neighbour city. There are some minor exceptions but this may explain why the bank is not opening a large number of branches.

And due to the fact that they have no own branches you rely for the withdrawel of the money on a wire transfer respectively the ATMs.

So it seems the DKB has a 1,75 % transaction fee for purchases using a foreign currency. Amex in Germany has (as far as I remember 2,0%) - therefore only a minor difference.

The genuine Lufthansa Miles&More Card (which is issued in Germany) has also 1,75 % foreign transaction fee. Also buying a Business package with a higher yearly fee reduces that to 1,25 %.

http://www.miles-and-more-kreditkart...redit_Card.pdf