Personally, I think the current behavior is more consistent with the name since it is the "user's preferences". (Don't know how it was documented prior to 10.5.3, so can't comment on that.)

But then it is strange that you need to use a Core Foundation API to access the global preferences when everything else is Cocoa. And writing to /Library/Preferences is even more awkward since you need a helper code that runs as root. Shouldn't there be some kind of service that manage this?

Just wondering…