Edit: SEE POSTS BELOW THIS ONE. Starwood changed it's terms (for the better) 3/1/2012 and any activity now counts.
Starwood Lurker posted the January 2012 terms
elsewhere (Terms were Revised March 2012):
3.2. You will be considered an "Active Member" so long as (a) your Membership has not been cancelled (by you or us), and (b) you have had an Eligible Stay at a Participating Property within the previous 12 months, or (c) you have earned Starpoints by using a Starwood Preferred Guest Credit Card during the previous 12 months. Starpoints resulting from transfers or earnings from Program affiliates do not count toward active status.
This would be why [in the past] SPG CC Cards & credited stays moved the points expiration date forward, but other activity like the trivia contests did not.