With CC minimums it's different, because they often have a transaction/processing fee as well (say $0.15 or $0.20) besides for the 1.5-3.5% fee, so for a $2 charge their CC processing overhead could be 10% of gross (and eat up their profits on low margin items).
+1
There is a big difference between them. When denying to accept amex, this means that they are here to squeeze out the most, not that they are looking at their earnings, and they see that they won't profit this way, Just
hakol revach. So, I think it's more important for me to make this purchase on amex to meet a spending requirement etc, than for him that he only want to earn another dollar. So I feel comfortable cornering him.
But, for small purchases, it's really not nice to corner them, they really lose from that. And we don't gain from that so much. Not to meet spending requirement, and even not for the stupid 5 points.