Well, we've got a good idea of the entire history of the GCN from launch to a couple weeks ago by way of Famitsu. Of course GCN eventually got into the hundreds, and PS3 is nowhere near that. However, looking at
GCN 2002 to compare to PS3 2007, here are some notables:
First time it hits below 10K: week of April 15
Number of weeks below 10K: 10
The lowest week I see is the week of May 20: 3,502
Notable bumps: 34K the week of March 18 (REmake), 32K the week of July 15 (Super Mario Sunshine)
Using the weeks from January 14 through the week of November 11 to find a non-holiday average for GCN's 2002, the average week was: 13.3 K