If a new node comes in with a rep of 0, then anyone who has a positive threshhold don't even see it, so until someone else does their duty, you are not even aware of it except as some footnote that there are messages under your threshold.
/. gets around this by a) restricting who can moderate at any time - hopefully they'll be reading with a low threshold, b) allowing posters to start with a positive "rep" (+1 for those logged in, more for higher level posters). Whether this model works for them, is it what we want here?
I'm being a bit specific to /. since that's where I have the most experience besides PM, but I'm sure you n think of other examples that fit my points.
...you might be eaten by a grue...