I have seen some packages having a separate NEWS file while there are many which don't. AFAIU it, having a NEWS.Debian.gz notes some very important/rare information as well as have possibly news about backward-compatibility going forward. This seems to be something in the DD's or DM's hand as there doesn't seem to be any info. in debian policy. Is there something that a prospective packager should look at ?  
Can 'NEWS' in a Debian package be made by the packager/maintainer?
debian;package management;debian policy
The NEWS files are documented in the Debian Developer's Reference. There is more background information in the mailing list thread which led to their creation.