I can't really comment on the curiosity of the particualar US rule - I have a feeling it partly turns on showing actual malice. We don't have that rule here in the UK and are only slowly developing branches of qualified privilege as defences for criticisms of politicians and officials and for "serious reportage". The Australians are ahead of us here.

We do however have a rule that a local authority itself (eg Derbyshire county council) cannot be defamed - at all.