It's interesting that the credit card companies seem to react negatively to putting your card into credit. Seeing as doing so gives them extra cash, reducing the amount of money they have to borrow at any given time. That's pretty much the idea of paying interest on deposit accounts - to encourage people to give their money to the bank!
The 28 degree card will sometimes be cancelled if you go into credit (for use as a fee free card overseas) more often than if used as a normal credit card.
I suspect the reason for this is that the 28 Degrees card aims to make a reasonable portion of their profit through people paying interest. A card with no annual fee, no currency conversion fees and no international transaction fees needs to have some other means of boosting profits, especially since it's generally not a card that people will put a large amount of spend on - hence they won't make much in transaction fees either. This card is aimed at people going on holiday overseas, who often spend a bit more than they expected/planned to do, so come back with a credit card bill they can't pay off straight away. So in this case, I suspect it's just that they don't want you as a customer if there is not at least a possibility that you might end up paying interest (and if you're never going into debit at all, then clearly you're never going to pay interest).
I don't think the same logic applies to the premium cards, which have high annual fees, high international transaction fees and in many cases currency conversion fees (or unfavourable rates). Those cards are clearly aimed at people who have relatively high incomes and who want to maximise points earn, and those people are generally not failing to pay off their balance each month.