It makes sense over the period of a day or so to avoid 100 simultaneous duplicate items, but beyond that it seems people are working around it all the time anyway.
I have no solution to propose, but the timing seems to be the most important factor for HN submissions, as we already know [1][2][3], and I think these small hacks are acceptable to work around the problem: reposts are not a big source of pollution, and users can report abusive behaviors with the flag button.
[1] http://hnpickup.appspot.com/
[3] http://jacquesmattheij.com/How+to+make+the+Hacker+News+homep...
I'm not bothered so much by reposts though I wonder if that was a factor too, attaching brand names
[1] https://developers.google.com/events/io/sessions/324149970