Credit Cards and their charges, page-4

Yep, I agree with you on most points, $1 in interest paid at 18% or 20% is $1 too much but there is nothing wrong with free credit. It enables me to keep minimal funds in our working account and transfer a larger amount once a month from other areas to pay the card bill on time. We purchase very few big ticket items and certainly not on the credit card.

They most certainly can change the rules at any time (with some reasonable notice) but they have always been able to do that and havn't so far. I am happy to give them loyalty while we are receiving something worthwhile in return.