To back Pogo up here, we had a comment earlier in the season that the upper threshold of 20% was too high for the AL/NL-only leagues, because the players we suggested were never available. So, whilst we haven't changed the threshold, we have tended to look for guys who are owned in the single-figure % as much as possible, so that there is a chance that they are available in these deeper leagues.
So, whilst Zimmerman does technically qualify to be mentioned, if he is
available in an NL-only league, there's probably something wrong with that league! (Either it's something like a 4-team league, or it's too uncompetitive).