I think the "Hydraulics Off" idea comes from the Robby world. Theory being that the collective doesnt rise when the hydros are switched off. At least thats what I was told when I did my rating a few years back. A fair few of the R44's here in NZ have a collective lock on them that helps mitigate the risk of a fly-away.
I have a question for the eurocopter guys.. With a squirrel (or twin squirrel in my case), will the machine be able to lift off with both engines at ground idle when empty? Seems to me that the collective lock is easy knocked off.