Xbox 360 NPD and our attach ratios are vastly different: Explanations?

[TWRoO]

TheSource said:

The holiday bundles for 360 add 5-10m units of sw which NPD would not count in the attach ratio.

360 has a base of 2m-3m units or so in Americas regions outside the USA which probably adds 10-15m.

The rest of it is just different ideas about legs I'd say.

but that also adds the extra 360 units, which means the attach ratio is largely unchanged.