If there's a law, it's a state law. Over the years, I've had the chance to become familiar with the laws of 6 or 8 states and none had such a requirement.
In my experience, it's purely bank policy and reflects some flexibility. If I die and you go to the visitation at the funeral home it's nonsensical at best for you to tell my spouse she needs to bring in a copy, certified at that, of the death certificate. If you didn't know me or go to visitation, then a photocopy of a certified copy should suffice.
Like any other piece of paper, you should require it because you need it, not because you like the look of a nice plump file.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.