Quote from rufus_4000:
In my opinion, this is an attempt on Merc's part to reverse the decrease in NQ volume. ES volume is still growing month to month. NQ volume, on the other hand, has lost much to ER (and YM, I believe). So, Merc will probably not mess with a success (ES), but will tinker with NQ.
Merc already tried to increase the messaging cancel / fill ratio for NQ to 10 : 1 (vs 5 : 1 for ES) during 4Q2005. This did not have any noticable affect on NQ volume (it continues to decrease), so now they are trying to reduce the tick size.