I think the same argument could be made: Because the bank doesn't post transactions on weekends or holidays, the customer would not have an opportunity to "stop the bleeding" by making a deposit on a Saturday or Sunday (or holiday), so why is the customer penalized for not curing the overdraft on those days?
Even if that argument doesn't hold up, it's important to note that some of the banks that have had problems with assessing penalties on non-business days have had disconnects between their customer communications (disclosures, brochures, advertising, etc.) and the actual operation of their systems. Or they have failed to explicitly say that fees would be imposed for non-business days when the balance remains negative.
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John S. Burnett
BankersOnline.com
Fighting for Compliance since 1976
Bankers' Threads User #8