One of the most trolled against aspects of the PS3 here on VGChartz must have been its software attach ratio, which would alledgedly be far inferior to that on the XBox 360. The XBox 360 had a one year headstart in the US and Japan and 1 year and 4 month in PAL regions, attach ratios should thus normally be compared taking equal timeframes as the fundamental question of course is: "Do PS3 owners buy fewer games than XBox 360 owners." Hence the average amount of software titles bought per month of console ownership.
With regard to the United States, the XBox 360 has a much bigger installbase at this point. However Sony was kind enough to point out that multi-platform blockbusters do sell relatively well on the PS3, selling more software units than one would expect based on installbase differences:
http://www.gamasutra.com/php-bin/news_index.php?story=23186
More interesting is Europe, according to VGChartz the XBox 360 installbase here in May 2009 was millions ahead of the PS3.
Now if we look at the European software sales of that period (based on GfK data):
Based on those figures combined with VGChartz data, the PS3 seems to show superior attach ratios for multi-platform games in early 2009 in Europe as well.
My conclusion: The fat PS3 wasn't widely used as just a Blu-Ray player as was often claimed by fanboys. First and foremost its a games console, selling impressive amounts of games.
Edit:
My assesment was correct. For the last reported fiscal year the PS3 sold 115.6 million units software units and the XBox 360 sold 103.1 million units. This while at the end of March 2010 Sony sold 4.47 fewer units to retail than the amount of XBox 360s shipped by Microsoft.
Meanwhile VGChartz has also already adjusted the PS3 install base up in Europe/others for the period before 2009.