As for for the legal role of the NOTICE file, I think there may be more complexity than that. Here, for example, we find Lawrence Rosen and Roy Fielding (among others) discussing what must go in NOTICE instead of in LICENSE: https://issues.apache.org/jira/browse/LEGAL-62
NOTICE files have special meaning in the Apache license. I misread (I was on my phone) and thought you were talking about copyright notice previously. Even Larry thinks that copyright notice is mostly worthless. However, you can't removes notices that currently exist unless you are the copyright owner, so they have rules for moving them to NOTICE files.
Again, you should not confuse organizational requirements and policies with what the law requires or recognizes.
Internal to Google, I have set requirements about the form of copyright notice/etc, for example. This isn't just because of legal requirements, but because it stops useless developer arguments and time wasting. Sanity and consistency are important in this kind of thing, and without rules folks have a penchant for starting mailing list arguments about it every few months.
Besides that, it also helps deal with the outside world. By having strict, sane, and consistent policies, dealing with corporate and other contributors becomes a lot easier.
They want to add 600 new copyright lines to your file, you point them to the policy that says no.