If Sony puts out the kind of better quality next gen games the system is capable of it to support the motion controller, it might be a better option for some folk, though perhaps not the most casual of the casual gaming crowd.
But imagine Wii-like games, Wii-like functionality on a gaming system that also plays Blu-ray, is a media server for viewing photos/playing music etc., and plays high quality next gen games--something for everyone in the family. A really nice upgrade for all those people that bought a Wii at $250 when the PS3 was $400-$500. Now as their Wii gathers dust, they look for the next thing. Meanwhile the Wii doesn't have anywhere else to go technology-wise unless Nintendo puts out a next gen version. I see this as a good marketing decision on Sony's part. It remains to be seen if they can pull it off of course.