Or how a bank is going " to get us" some way - some day. That's a nonsensical argument.
Sure they are. Here's an example from back in 2005 or so:
I had a citi card. Statement generated on the 10th of the month. I log on on the 11th, see my balance, pay it off.
A charge from the 9th was floating around for a while and hit the card later, giving me a statement balance of five bucks for that billing cycle.
My dingbat wife loses her wallet, I call citi and cancel the card in order to get a new one etc.
They take their time sending a new one. Meanwhile they lock me out of my online account "because of fraud."
Then to reopen my online account I need them to snail-mail me a password.
Then because my account is "new" they only let me pay $1000, not the entire balance, in case I'm using a hijacked checking account.
Long story short, they did the two-month averaging thing and charged me five bucks interest on a five dollar balance.
Could I have done some things differently? Absolutely. But it's a game where the house has all the advantages.