Considering Wii Fit has already sold 20 million copies, i think Wii sports would have sold 30-35 million by now.
WiiFit was bundled with new revolutionary hardware (The Balance Board), WiiSports was nothing more then an interesting tech demo. To be honest as a launch title and its lifespan till today I'd expect around 10-million in sales maybe a tad more. I think WiiSports Resort bundled with WiiMotionPlus will answer the question, we will be able to see how well WiiSportsResort sells and based on that can see how well WiiSports may have sold had it not been bundled.
I know I for one am considering getting my WiiMotionPlus bundled with RedSteel2 rather then getting WiiSportsResort. I think WiiSportsResort will sell well thanks to the publicity WiiSports has thanks to it being bundled. In the end WiiSports was a cheaply developed tech demo and WiiSports Resort is while not as small as WiiSports still cheaply developed.
The main thing we can be sure of, Nintendo is going to make a fortune for very little effort. Unfortunetly it goes to show you that Nintendo is getting lazy. No longer launching multi-year big budget titles instead opting for smaller month to year long tech demo's!
"In God We Trust - In Games We Play " - Joel Reimer