IF Natal really works and it gets compelling software to make use of it, it will indeed have a chance at attracting new audiences - those that do not want any controller at all.
For example the fitness crowd - EA Sports Active for example would be an even better exergame if I didn't have to use any controller, as quite frankly controllers are somewhat of a bother for this type of game - but ONLY IF Natal will follow my exact movements and recognize any errors I make in real time, correcting me when it needs to and correctly estimating how much effort I put in all the time (these functions are presently covered by the Wiimote and Nunchuk).
On the other hand I don't see any reason for the Gem to attract new audiences into gaming that the Wii hasn't reached.
Currently Playing: Shin Megami Tensei: Devil Survivor Overclocked, Professor Layton and the Curious Village
Anticipating: Xenoblade, The Last Story, Mario Kart 7, Rayman Origins, Zelda SS, Crush3D, Tales of the Abyss 3DS, MGS:Snake Eater 3DS, RE:Revelations, Time Travellers, Professor Layton vs. Ace Attorney, Luigi's Mansion 2, MH TriG, DQ Monsters, Heroes of Ruin