Wii is successful because of first party support. 3rd party motion control developers dont do much to boost the Wii, so i dont see them boosting the 360 and PS3 much either. They'll get a piece of the cake, but it wont do much for sales imo.
So both the Move and Natal will need a strong first party support to be successful, and imo (again) the Move feels like it will come with a strong initial amount of games but drop quite fast. Natal will be more casual and with an already lack of first party, i dont see Natal receiving any more support than the 360 has today.
So in conclusion, both will have very low impact on overall sales, but will receive some action from Wii developers. Move might get more support from 3rd party Wii developers due to similarities with the Wii.
