Kinda expected for Wii as more mainstream console to have less "active" users, unlikely it tops this graph anytime soon if ever . Though Nielsen didn't specify who are "active" users? Obvious guess, someone who play particular home console more than X hours\minutes per week\day. The real question is... X = ?
At "Usage Mintues Percentage" graph Wii is high due to massive userbase, though lower than it was earlier (if my memory doesn fail, last survey cover H2 2008 time period), when it actually was on top of X360, little lower than PS2. The lack of software releases and unsatisfactory results of AC: City Folk and Wii Music (as Iwata said) lead not only to diminishing hardware sales but also to fewer active gamers in H1 2009. My guess, Wii will be on top of the "Usage Mintues Percentage" graph at the end of 2009.
Though "Console usage by Gender" graph is weird. My common sense says me that PS2, X360 and Wii graphs are believable at least, but PS3, Xbox and GC male\female percentage is total BS. I'm curious what were the questions they asked in the survey to get this kind of data?
BTW Here's results of previous Nielsen survey "Usage Minutes Percentage", PS2 flat, X360 up, Wii down:
