ok. get it now.
guess it's up to the LL owner - and in my mind they should make a decision based on how often does the vast majority of the bookmarkers return? do a high percentage of them (say 70%?) come back on a weekly basis? Then 7 days is probably enough. Do they come back every two weeks? Then 14 days
Guess a script could also be forged, which would strip away the NEW stars from a certain site for each particular surfer once the surfer clicked on it (got it displayed to him x times?).
Also this probably has to do with how many sites get added daily to that category. Some LL's have like 10 sites/page and your site could be qualified as new forever and it won't do you any good since it's buried on page 17. Others have just 1 page for each category and they never delete a site once it gets accepted - in which case the NEW stars are always good to have, to distinct your site from the crowd.
From a submiter POV, I've to be happy with what I get.
Of course, more is always better @ this sort of thing