There is an easy explanation to how attach rates work and why they are higher later in cycle of the system.
Ex:
Month 1:
360 (300k hardware), (1.5 mil software)
Wii (600k hardware), (1.5 mil software)
Month 2:
360 (300k hardware), (1.5 mil software)
Wii (600k hardware), (1.5 mil software)
Now if you look at attach rate what do you see for the 360
600k units and 3 million software, so attach rate of 5:1
and for the Wii you see
1.2 million units and 3 million software, so attach rate of 2.5:1
By selling half the hardware as the Wii yet the same software the attach ration will be double that of the Wii. Its common sense the faster a console is growing the slower its attach rate will grow. They are both selling the same amount of software and thats all the software programmers care about. Who gives a shit is only 1/10 of owners buy my game vs 1/4 if it is the same number.