Clearly both are indeed taking that risk. Quick summary of my views on each:
PS3 Plus points
Eyetoy already in place with at least some of the install base so there should be immediate install base for the wand to appeal to
Physical controllers with camera is better for gaming than Natal (IMO)
Stronger brand still than 360 with general consume
PS3 Negatives
Poor Sony history with adding peripherals like this
Visual look unknown - will they get the final wand design right?
360 Plus points
Most 'hype catching' tech
Strong presence in US, with a lot of services Natal can built on plus the games
Easy to grasp concept - place device on TV and off you go
360 Negatives
Weakest tech for games (again IMO) - if they stick to no controllers, which I doubt they will but for the moment I'll take them at face value
Unproven experience with this kind of peripheral
Weaker brand for 'casual' demographic and gamer, particularly for the types of games, experiences shown so far
I'd note I hate the 'casual' term but use it for simplicity.
All said, I think both are roughly even, with perhaps Sony having a slight edge on Brand recognition in the WW market. The real test, as you say, is the games. Both might get this right, or only one.
If they both get it right and both peripherals sell well then neither will see much advantage from them. If one messes up the games and the other doesn't... then it could get interesting.
Try to be reasonable... its easier than you think...
