Symlinks are a poor example, IMO. Yes, they need to be carefully handled for security reasons. But they also offer great flexibility that is actually widely used, and that wouldn't be available through other mechanisms.
I rest my case. ;-)
What do we gain from having NUL everywhere, as opposed to having it in only one specific location, e.g. root?
Also, as an aside, I thought it wasn't a magic file (nul), but rather a magic device (NUL:), which IMO makes a lot of sense.