"Natal appeared to me to be a technological solution in search of a problem," said Creutz. "I had a very hard time envisioning playing Modern Warfare 3 using Natal," he said, adding, "By contrast, I had a very easy time envisioning it (and enjoying it) using Sony's control/motion capture scheme." Creutz stated that Microsoft is likely trying to snag some of the Wii's casual marketshare -- "a difficult proposition given that you're essentially asking casual gamers to upgrade twice during the cycle," according to Creutz -- while Sony's device caters more to the core gaming demographic.
We must point out that neither Project Natal nor the PlayStation Motion Controller are finished products, so there's no telling how they might be implemented in future games. For example, there's no reason that Natal couldn't make use of both motion sensing and traditional control, similar to Sony's device. Furthermore, we'd say Sony is probably just as keen to capture some of the casual market as Microsoft.
Sony PlayStation Move motion controller
Microsoft Xbox 360
Sony PlayStation 3 (late 2012)
Microsoft Xbox One