Quick, someone call the Nintendo fanboy fire dept! All is not perfect in Wii-land! Spin the Wii's low attach rate into something that looks better than the other consoles! =)
Seriously though, the Wii's attach rate being kinda low is not new news. No one has ever really been able to explain it -- you're certainly not going to get an explanation from the Nintendo fans here... just some spin and a lot of pretending and excuses.
I think the general concensus of the non-blind, non-fanboy is that "Blue Ocean" just doesn't equate with "Gaming addict".. and hence you get a lower attach rate with that strategy. C'est la vie. Works good for Nintendo, so they aren't complaining.