Another big thing to look at is attach rates. These numbers are a bit outdated but it's the best I can do. Through December 2006:
The PS3 has an attach rate of 2.8 games sold per console worldwide. At the Japanese launch, it had a rate of below 1 (0.98 ) and at the US launch the rate was 1.5 games/console.
The Wii, in the same time period(which does not include the ~1.5 million in Virtual Console sales or the pack-in Wii Sports for non-Japan areas,) has an attach rate of 5.5 games/console. At launch, the rate was 1.8 in Japan, 1.5 in Australia, and 3.0 in America (I can't find solid European figures.)
Developers are paying attention to this. It may be because there are no PS3 games worth buying - but the PS3's competition both have attach rates above 5 and climbing while the PS3 is stuck at below 3. Low attach rates = low sales = low developer profits = we don't want to make things for you no more.
The real battle will be next winter. Microsoft will have Halo 3(and could price drop,) Nintendo could hold Mario Galaxy or any number of first/third party games for the holidays. Sony NEEDS Square or Konami or SOMEONE to come through with a AAA, must-buy title for Holiday 2007 and it needs to be good enough to move a $600 console. They swung and missed at launch, they swung and missed at the post-holiday fallout, and Holiday 2007 may be their only chance to right the ship. And I'm not sure if placing second will be enough.