Also, it should be noted that while the percentage growths are the same, the X360 has had a lower relative installbase increase than its competition.
The X360 installbase has had a roughly 55% increase
The Ps3 has had a roughly 70% increase
The Wii installbase has had a roughly 80% increase
So the Wii and Ps3 should have increased more software wise than the X360
Note: These numbers are rough estimates.
Edit: I may seem a bit offensive - but truly, this is a great thread! It has a lot of interesting info, and something people usually forget.