I thought the 360 was actually doing quite well, and certainly upthere with the Wii in terms of overall game revenue? They have to be close, if you approximate the 360 having twice the attach rate, with half the consoles...
Trying to find reliable attach rates seems to be difficult. The rates for the 360 seem to vary between 5 and 7, for the wii between 5.5 and 8, with the PS3 around 3-4. It gets even harder if you stop looking at company statements, as there's a lot of debate about whose sampling is flawed.
I certainly wouldn't say the 360 has twice the attach rate of the Wii though. And don't forget that Nintendo have made a profit on every Wii sold, whereas MS were selling them at a loss for a good while. I doubt the revenue is that comparable.
But the Wii is the standout console this generation, for whatever reasons we care not to understand, it's flying off shelves and can only be described as as a run away success...
Which is the bottom line, the wii attracts attention like neither of the other consoles from people who normally couldn't care less, and that's where Nintendo are cleaning up. Instead of just fighting over the core market, they broadened it, and that's the big difference.