"Versus mode was a bit too dangerous," Fighters Uncaged producer Luc Verdier said when asked about a competitive mode for his newly announced Kinect-enabled fighting game. "It's possible to do, but people just end up hitting each other." Thus, the game's only multiplayer mode is a cooperative battle, where two players work together against the artificial intelligence.
Of course, people don't usually end up killing one another while playing games like Just Dance, even if four players are moving about in an enclosed space. But Verdier said motion-controlled games where multiple players are synchronized are safer than games where the players can just "do whatever." We'd also hazard to guess that dancing players just tend to be less intentionally violent than fighting game players, especially when those fighting game players are actively playing.