According to the original NPD report, the Wii was not in the top 3 most used hours per week meaning it must be under the PS3's 5.8 hours per week average. But I do admit that the NPD has some explaining to do as the numbers are inconsistent with the overall average they listed of 8.0 hours per week. If X360 is the highest average at 7.3 hours, then it is impossible to have an industry average of anything higher than 7.3 hours.
I will note that Wii may not be used as much online per person but that it does have the second most online users of the 3 consoles in the US.
X360 at 48% = 10.6 million
PS3 at 30% = 3.9 million
Wii at 30% = 9.6 million
Now if the same data is applied globally (not a very accurate extrapolation, mind you), we get the following:
X360 at 48% = 18.37 million
PS3 at 30% = 9.75 million
Wii at 30% = 20.46 million