360 is console with highest attach rate, says Gamasutra
Gamasutra's posted a piece claiming 360 has the highest attach rate of the current gen machines, with about 6.5 games sold per console.
Wii comes next, apparently, with around 5.5 games per machine, and PS3 has the lowest attach rate at round 5.2.
The data's based on each machine's position after 23 months at market, and there's a graph there showing first- and third-party split.
Take a look.