If there were demos, I'm willing to bet less people would have bought The Conduit..
Demos for third party games on the Wii would actually hurt sales in most cases. People buying the cat in the bag is one the saving graces for third parties.
That may have been true in the beginning (up to a year ago or so), but personally I believe that now it is hurting sales sine a lot of people probably became warry of buying new games at full price after getting burned.
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