Encryption keys in a TPM? RAID configurations which depend on physical cabling setups? Storage that can't be physically removed? There are a thousand ways that taking the "hard drive" from a computer will end up losing information that would be recoverable with the whole device. It's not really reasonable to expect police departments to do IT foresics on site during a search.

That doesn't mean that the seizure is "justified", but there are no simple answers either.