> I vaguely recall something about how the US has specific laws allowing certain requests to be ignored (or maybe even criminalising the sending of) generated or form-letters, due apparently to this sort of abuse.
Exactly, and it is abuse. There are so called 'mass letter writers' here in NL that keep on sending FOI requests and other letters to local government effectively DDOSing the services and they too can be - and have been - slapped down.